diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index fa98d80..18a96d1 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -377,6 +377,9 @@
     const char *test;
     const char *filename;
     int line_no;
+#if defined(MBEDTLS_TEST_MUTEX_USAGE)
+    const char *mutex_usage_error;
+#endif
 }
 test_info;
 
@@ -784,11 +787,49 @@
     return ret;
 }
 
+#if defined(MBEDTLS_TEST_MUTEX_USAGE)
 /** Mutex usage verification framework.
  *
+ * The mutex usage verification code below aims to detect bad usage of
+ * Mbed TLS's mutex abstraction layer at runtime. Note that this is solely
+ * about the use of the mutex itself, not about checking whether the mutex
+ * correctly protects whatever it is supposed to protect.
+ *
+ * The normal usage of a mutex is:
+ * ```
+ * digraph mutex_states {
+ *   "UNINITIALIZED"; // the initial state
+ *   "IDLE";
+ *   "FREED";
+ *   "LOCKED";
+ *   "UNINITIALIZED" -> "IDLE" [label="init"];
+ *   "FREED" -> "IDLE" [label="init"];
+ *   "IDLE" -> "LOCKED" [label="lock"];
+ *   "LOCKED" -> "IDLE" [label="unlock"];
+ *   "IDLE" -> "FREED" [label="free"];
+ * }
+ * ```
+ *
+ * All bad transitions that can be unambiguously detected are reported.
+ * An attempt to use an uninitialized mutex cannot be detected in general
+ * since the memory content may happen to denote a valid state. For the same
+ * reason, a double init cannot be detected.
+ * All-bits-zero is the state of a freed mutex, which is distinct from an
+ * initialized mutex, so attempting to use zero-initialized memory as a mutex
+ * without calling the init function is detected.
+ *
+ * If an error is detected, this framework will report what happened and the
+ * test case will be marked as failed. Unfortunately, the error report cannot
+ * indicate the exact location of the problematic call. To locate the error,
+ * use a debugger and set a breakpoint on mbedtls_test_mutex_usage_error().
  */
+enum value_of_mutex_is_valid
+{
+    MUTEX_FREED = 0, //!< Set by threading_mutex_free_pthread
+    MUTEX_IDLE = 1, //!< Set by threading_mutex_init_pthread and by our unlock
+    MUTEX_LOCKED = 2, //!< Set by our lock
+};
 
-#if defined(MBEDTLS_TEST_MUTEX_USAGE)
 typedef struct
 {
     void (*init)( mbedtls_threading_mutex_t * );
@@ -798,6 +839,19 @@
 } mutex_functions_t;
 static mutex_functions_t mutex_functions;
 
+static void mbedtls_test_mutex_usage_error( mbedtls_threading_mutex_t *mutex,
+                                            const char *msg )
+{
+    (void) mutex;
+    if( test_info.mutex_usage_error == NULL )
+        test_info.mutex_usage_error = msg;
+    mbedtls_fprintf( stdout, "[mutex: %s] ", msg );
+    /* Don't mark the test as failed yet. This way, if the test fails later
+     * for a functional reason, the test framework will report the message
+     * and location for this functional reason. If the test passes,
+     * mbedtls_test_mutex_usage_check() will mark it as failed. */
+}
+
 static void mbedtls_test_wrap_mutex_init( mbedtls_threading_mutex_t *mutex )
 {
     mutex_functions.init( mutex );
@@ -805,18 +859,67 @@
 
 static void mbedtls_test_wrap_mutex_free( mbedtls_threading_mutex_t *mutex )
 {
+    switch( mutex->is_valid )
+    {
+        case MUTEX_FREED:
+            mbedtls_test_mutex_usage_error( mutex, "free without init or double free" );
+            break;
+        case MUTEX_IDLE:
+            /* Do nothing. The underlying free function will reset is_valid
+             * to 0. */
+            break;
+        case MUTEX_LOCKED:
+            mbedtls_test_mutex_usage_error( mutex, "free without unlock" );
+            break;
+        default:
+            mbedtls_test_mutex_usage_error( mutex, "corrupted state" );
+            break;
+    }
     mutex_functions.free( mutex );
 }
 
 static int mbedtls_test_wrap_mutex_lock( mbedtls_threading_mutex_t *mutex )
 {
     int ret = mutex_functions.lock( mutex );
+    switch( mutex->is_valid )
+    {
+        case MUTEX_FREED:
+            mbedtls_test_mutex_usage_error( mutex, "lock without init" );
+            break;
+        case MUTEX_IDLE:
+            if( ret == 0 )
+                mutex->is_valid = 2;
+            break;
+        case MUTEX_LOCKED:
+            mbedtls_test_mutex_usage_error( mutex, "double lock" );
+            break;
+        default:
+            mbedtls_test_mutex_usage_error( mutex, "corrupted state" );
+            break;
+    }
     return( ret );
 }
 
 static int mbedtls_test_wrap_mutex_unlock( mbedtls_threading_mutex_t *mutex )
 {
-    return( mutex_functions.unlock( mutex ) );
+    int ret = mutex_functions.unlock( mutex );
+    switch( mutex->is_valid )
+    {
+        case MUTEX_FREED:
+            mbedtls_test_mutex_usage_error( mutex, "unlock without init" );
+            break;
+        case MUTEX_IDLE:
+            mbedtls_test_mutex_usage_error( mutex, "unlock without lock" );
+            break;
+        case MUTEX_LOCKED:
+            if( ret == 0 )
+                mutex->is_valid = MUTEX_IDLE;
+            break;
+        default:
+            mbedtls_test_mutex_usage_error( mutex, "corrupted state" );
+            break;
+    }
+    return( ret );
 }
 
 static void mbedtls_test_mutex_usage_init( void )
@@ -831,4 +934,16 @@
     mbedtls_mutex_unlock = &mbedtls_test_wrap_mutex_unlock;
 }
 
+static void mbedtls_test_mutex_usage_check( void )
+{
+    if( test_info.mutex_usage_error != NULL &&
+        test_info.result != TEST_RESULT_FAILED )
+    {
+        /* Functionally, the test passed. But there was a mutex usage error,
+         * so mark the test as failed after all. */
+        test_fail( "Mutex usage error", __LINE__, __FILE__ );
+    }
+    test_info.mutex_usage_error = NULL;
+}
+
 #endif /* MBEDTLS_TEST_MUTEX_USAGE */
diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index 9f36690..2aecf81 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -176,6 +176,10 @@
 #else
     fp( params );
 #endif
+
+#if defined(MBEDTLS_TEST_MUTEX_USAGE)
+    mbedtls_test_mutex_usage_check( );
+#endif /* MBEDTLS_TEST_MUTEX_USAGE */
 }
 
 /**