diff --git a/tests/site_scons/platforms/avr/avr.py b/tests/site_scons/platforms/avr/avr.py
index 4621a32..f0a8cc9 100644
--- a/tests/site_scons/platforms/avr/avr.py
+++ b/tests/site_scons/platforms/avr/avr.py
@@ -11,7 +11,8 @@
     env.Replace(TEST_RUNNER = "build/run_test")
     env.Append(CFLAGS = "-mmcu=atmega1284 -Dmain=app_main -Os")
     env.Append(CXXFLAGS = "-mmcu=atmega1284 -Dmain=app_main -Os")
-    env.Append(CPPDEFINES = {'PB_CONVERT_DOUBLE_FLOAT': 1, 'UNITTESTS_SHORT_MSGS': 1, '__ASSERT_USE_STDERR': 1})
+    env.Append(CPPDEFINES = {'PB_CONVERT_DOUBLE_FLOAT': 1, 'UNITTESTS_SHORT_MSGS': 1,
+                             '__ASSERT_USE_STDERR': 1, 'MAX_REALLOC_SIZE': '4096'})
     env.Append(LINKFLAGS = "-mmcu=atmega1284")
     env.Append(LINKFLAGS = "build/avr_io.o -Wl,-Map,avr.map")
     avr_io = env.Object("build/avr_io.o", "site_scons/platforms/avr/avr_io.c")