diff --git a/tests/include/test/memory.h b/tests/include/test/memory.h
index e043751..181280f 100644
--- a/tests/include/test/memory.h
+++ b/tests/include/test/memory.h
@@ -69,7 +69,7 @@
  *  unset in the test wrappers so that calls to PSA functions from the library
  *  do not poison memory.
  */
-extern _Thread_local int mbedtls_test_memory_poisoning_enabled;
+extern _Thread_local unsigned int mbedtls_test_memory_poisoning_count;
 
 /** Poison a memory area so that any attempt to read or write from it will
  * cause a runtime failure.
@@ -79,7 +79,7 @@
 void mbedtls_test_memory_poison(const unsigned char *ptr, size_t size);
 #define MBEDTLS_TEST_MEMORY_POISON(ptr, size)    \
     do { \
-        mbedtls_test_memory_poisoning_enabled = 1; \
+        mbedtls_test_memory_poisoning_count++; \
         mbedtls_test_memory_poison(ptr, size); \
     } while (0)
 
@@ -94,7 +94,7 @@
 #define MBEDTLS_TEST_MEMORY_UNPOISON(ptr, size)    \
     do { \
         mbedtls_test_memory_unpoison(ptr, size); \
-        mbedtls_test_memory_poisoning_enabled = 0; \
+        mbedtls_test_memory_poisoning_count--; \
     } while (0)
 
 #else /* MBEDTLS_TEST_MEMORY_CAN_POISON */
diff --git a/tests/src/test_memory.c b/tests/src/test_memory.c
index dbb7b20..ac9dde6 100644
--- a/tests/src/test_memory.c
+++ b/tests/src/test_memory.c
@@ -20,7 +20,7 @@
 
 #if defined(MBEDTLS_TEST_MEMORY_CAN_POISON)
 
-_Thread_local int mbedtls_test_memory_poisoning_enabled = 0;
+_Thread_local unsigned int mbedtls_test_memory_poisoning_count = 0;
 
 static void align_for_asan(const unsigned char **p_ptr, size_t *p_size)
 {
@@ -39,7 +39,7 @@
 
 void mbedtls_test_memory_poison(const unsigned char *ptr, size_t size)
 {
-    if (!mbedtls_test_memory_poisoning_enabled) {
+    if (mbedtls_test_memory_poisoning_count == 0) {
         return;
     }
     if (size == 0) {