diff --git a/ChangeLog.d/issue4630.txt b/ChangeLog.d/issue4630.txt
new file mode 100644
index 0000000..0bc4b99
--- /dev/null
+++ b/ChangeLog.d/issue4630.txt
@@ -0,0 +1,2 @@
+Bugfix
+   * Stop using reserved identifiers as local variables. Fixes #4630.
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 5187d86..7fef599 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -826,14 +826,14 @@
  * \param E        The exponent MPI. This must point to an initialized MPI.
  * \param N        The base for the modular reduction. This must point to an
  *                 initialized MPI.
- * \param _RR      A helper MPI depending solely on \p N which can be used to
+ * \param prec_RR  A helper MPI depending solely on \p N which can be used to
  *                 speed-up multiple modular exponentiations for the same value
  *                 of \p N. This may be \c NULL. If it is not \c NULL, it must
  *                 point to an initialized MPI. If it hasn't been used after
  *                 the call to mbedtls_mpi_init(), this function will compute
- *                 the helper value and store it in \p _RR for reuse on
+ *                 the helper value and store it in \p prec_RR for reuse on
  *                 subsequent calls to this function. Otherwise, the function
- *                 will assume that \p _RR holds the helper value set by a
+ *                 will assume that \p prec_RR holds the helper value set by a
  *                 previous call to mbedtls_mpi_exp_mod(), and reuse it.
  *
  * \return         \c 0 if successful.
@@ -845,7 +845,7 @@
  */
 int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
                          const mbedtls_mpi *E, const mbedtls_mpi *N,
-                         mbedtls_mpi *_RR );
+                         mbedtls_mpi *prec_RR );
 
 /**
  * \brief          Fill an MPI with a number of random bytes.
diff --git a/library/bignum.c b/library/bignum.c
index dfc78c9..42ec7ac 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1587,17 +1587,17 @@
  */
 int mbedtls_mpi_add_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint b )
 {
-    mbedtls_mpi _B;
+    mbedtls_mpi B;
     mbedtls_mpi_uint p[1];
     MPI_VALIDATE_RET( X != NULL );
     MPI_VALIDATE_RET( A != NULL );
 
     p[0] = ( b < 0 ) ? -b : b;
-    _B.s = ( b < 0 ) ? -1 : 1;
-    _B.n = 1;
-    _B.p = p;
+    B.s = ( b < 0 ) ? -1 : 1;
+    B.n = 1;
+    B.p = p;
 
-    return( mbedtls_mpi_add_mpi( X, A, &_B ) );
+    return( mbedtls_mpi_add_mpi( X, A, &B ) );
 }
 
 /*
@@ -1605,17 +1605,17 @@
  */
 int mbedtls_mpi_sub_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint b )
 {
-    mbedtls_mpi _B;
+    mbedtls_mpi B;
     mbedtls_mpi_uint p[1];
     MPI_VALIDATE_RET( X != NULL );
     MPI_VALIDATE_RET( A != NULL );
 
     p[0] = ( b < 0 ) ? -b : b;
-    _B.s = ( b < 0 ) ? -1 : 1;
-    _B.n = 1;
-    _B.p = p;
+    B.s = ( b < 0 ) ? -1 : 1;
+    B.n = 1;
+    B.p = p;
 
-    return( mbedtls_mpi_sub_mpi( X, A, &_B ) );
+    return( mbedtls_mpi_sub_mpi( X, A, &B ) );
 }
 
 /** Helper for mbedtls_mpi multiplication.
@@ -2027,16 +2027,16 @@
                          const mbedtls_mpi *A,
                          mbedtls_mpi_sint b )
 {
-    mbedtls_mpi _B;
+    mbedtls_mpi B;
     mbedtls_mpi_uint p[1];
     MPI_VALIDATE_RET( A != NULL );
 
     p[0] = ( b < 0 ) ? -b : b;
-    _B.s = ( b < 0 ) ? -1 : 1;
-    _B.n = 1;
-    _B.p = p;
+    B.s = ( b < 0 ) ? -1 : 1;
+    B.n = 1;
+    B.p = p;
 
-    return( mbedtls_mpi_div_mpi( Q, R, A, &_B ) );
+    return( mbedtls_mpi_div_mpi( Q, R, A, &B ) );
 }
 
 /*
@@ -2297,7 +2297,7 @@
  */
 int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
                          const mbedtls_mpi *E, const mbedtls_mpi *N,
-                         mbedtls_mpi *_RR )
+                         mbedtls_mpi *prec_RR )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t wbits, wsize, one = 1;
@@ -2365,17 +2365,17 @@
     /*
      * If 1st call, pre-compute R^2 mod N
      */
-    if( _RR == NULL || _RR->p == NULL )
+    if( prec_RR == NULL || prec_RR->p == NULL )
     {
         MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &RR, 1 ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_shift_l( &RR, N->n * 2 * biL ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &RR, &RR, N ) );
 
-        if( _RR != NULL )
-            memcpy( _RR, &RR, sizeof( mbedtls_mpi ) );
+        if( prec_RR != NULL )
+            memcpy( prec_RR, &RR, sizeof( mbedtls_mpi ) );
     }
     else
-        memcpy( &RR, _RR, sizeof( mbedtls_mpi ) );
+        memcpy( &RR, prec_RR, sizeof( mbedtls_mpi ) );
 
     /*
      * W[1] = A * R^2 * R^-1 mod N = A * R mod N
@@ -2523,7 +2523,7 @@
     mbedtls_mpi_free( &W[1] ); mbedtls_mpi_free( &T ); mbedtls_mpi_free( &Apos );
     mbedtls_mpi_free( &WW );
 
-    if( _RR == NULL || _RR->p == NULL )
+    if( prec_RR == NULL || prec_RR->p == NULL )
         mbedtls_mpi_free( &RR );
 
     return( ret );