diff --git a/portable/ARMv8M/non_secure/port.c b/portable/ARMv8M/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/ARMv8M/non_secure/port.c
+++ b/portable/ARMv8M/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM23/non_secure/port.c b/portable/GCC/ARM_CM23/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM23/non_secure/port.c
+++ b/portable/GCC/ARM_CM23/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM23_NTZ/non_secure/port.c b/portable/GCC/ARM_CM23_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM23_NTZ/non_secure/port.c
+++ b/portable/GCC/ARM_CM23_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM33/non_secure/port.c b/portable/GCC/ARM_CM33/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM33/non_secure/port.c
+++ b/portable/GCC/ARM_CM33/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM33_NTZ/non_secure/port.c b/portable/GCC/ARM_CM33_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM33_NTZ/non_secure/port.c
+++ b/portable/GCC/ARM_CM33_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM35P/non_secure/port.c b/portable/GCC/ARM_CM35P/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM35P/non_secure/port.c
+++ b/portable/GCC/ARM_CM35P/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM35P_NTZ/non_secure/port.c b/portable/GCC/ARM_CM35P_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM35P_NTZ/non_secure/port.c
+++ b/portable/GCC/ARM_CM35P_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM55/non_secure/port.c b/portable/GCC/ARM_CM55/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM55/non_secure/port.c
+++ b/portable/GCC/ARM_CM55/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM55_NTZ/non_secure/port.c b/portable/GCC/ARM_CM55_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM55_NTZ/non_secure/port.c
+++ b/portable/GCC/ARM_CM55_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM85/non_secure/port.c b/portable/GCC/ARM_CM85/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM85/non_secure/port.c
+++ b/portable/GCC/ARM_CM85/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/GCC/ARM_CM85_NTZ/non_secure/port.c b/portable/GCC/ARM_CM85_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/GCC/ARM_CM85_NTZ/non_secure/port.c
+++ b/portable/GCC/ARM_CM85_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM23/non_secure/port.c b/portable/IAR/ARM_CM23/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM23/non_secure/port.c
+++ b/portable/IAR/ARM_CM23/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM23_NTZ/non_secure/port.c b/portable/IAR/ARM_CM23_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM23_NTZ/non_secure/port.c
+++ b/portable/IAR/ARM_CM23_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM33/non_secure/port.c b/portable/IAR/ARM_CM33/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM33/non_secure/port.c
+++ b/portable/IAR/ARM_CM33/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM33_NTZ/non_secure/port.c b/portable/IAR/ARM_CM33_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM33_NTZ/non_secure/port.c
+++ b/portable/IAR/ARM_CM33_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM35P/non_secure/port.c b/portable/IAR/ARM_CM35P/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM35P/non_secure/port.c
+++ b/portable/IAR/ARM_CM35P/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM35P_NTZ/non_secure/port.c b/portable/IAR/ARM_CM35P_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM35P_NTZ/non_secure/port.c
+++ b/portable/IAR/ARM_CM35P_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM55/non_secure/port.c b/portable/IAR/ARM_CM55/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM55/non_secure/port.c
+++ b/portable/IAR/ARM_CM55/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM55_NTZ/non_secure/port.c b/portable/IAR/ARM_CM55_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM55_NTZ/non_secure/port.c
+++ b/portable/IAR/ARM_CM55_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM85/non_secure/port.c b/portable/IAR/ARM_CM85/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM85/non_secure/port.c
+++ b/portable/IAR/ARM_CM85/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */
diff --git a/portable/IAR/ARM_CM85_NTZ/non_secure/port.c b/portable/IAR/ARM_CM85_NTZ/non_secure/port.c
index 0490101..e027b21 100644
--- a/portable/IAR/ARM_CM85_NTZ/non_secure/port.c
+++ b/portable/IAR/ARM_CM85_NTZ/non_secure/port.c
@@ -754,8 +754,15 @@
     }
     #endif /* configUSE_TICKLESS_IDLE */
 
-    /* Stop and reset the SysTick. */
-    portNVIC_SYSTICK_CTRL_REG = 0UL;
+    /* Stop and reset SysTick.
+     *
+     * QEMU versions older than 7.0.0 contain a bug which causes an error if we
+     * enable SysTick without first selecting a valid clock source. We trigger
+     * the bug if we change clock sources from a clock with a zero clock period
+     * to one with a nonzero clock period and enable Systick at the same time.
+     * So we configure the CLKSOURCE bit here, prior to setting the ENABLE bit.
+     * This workaround avoids the bug in QEMU versions older than 7.0.0. */
+    portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG;
     portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
 
     /* Configure SysTick to interrupt at the requested rate. */