diff --git a/arch/arm/src/kinetis/kinetis_i2c.c b/arch/arm/src/kinetis/kinetis_i2c.c
index 88fef0f2fa..6efc2ff09a 100644
--- a/arch/arm/src/kinetis/kinetis_i2c.c
+++ b/arch/arm/src/kinetis/kinetis_i2c.c
@@ -150,6 +150,7 @@ static inline void kinetis_i2c_sem_post(struct kinetis_i2cdev_s *priv);
 /* Signal Helper */
 
 static inline void kinetis_i2c_endwait(struct kinetis_i2cdev_s *priv);
+static inline void kinetis_i2c_wait(struct kinetis_i2cdev_s *priv);
 
 /* I2C helpers */
 
@@ -368,6 +369,19 @@ static inline void kinetis_i2c_sem_post(struct kinetis_i2cdev_s *priv)
   sem_post(&priv->mutex);
 }
 
+/************************************************************************************
+ * Name: kinetis_i2c_wait
+ *
+ * Description:
+ *   Wait on the signaling semaphore
+ *
+ ************************************************************************************/
+
+static inline void kinetis_i2c_wait(struct kinetis_i2cdev_s *priv)
+{
+  sem_wait(&priv->wait);
+}
+
 /************************************************************************************
  * Name: kinetis_i2c_endwait
  *
@@ -1160,7 +1174,7 @@ static int kinetis_i2c_transfer(struct i2c_master_s *dev,
 
       wd_start(priv->timeout, I2C_TIMEOUT, kinetis_i2c_timeout, 1,
                (uint32_t) priv);
-      kinetis_i2c_endwait(priv);
+      kinetis_i2c_wait(priv);
 
       wd_cancel(priv->timeout);
 
diff --git a/sched/pthread/pthread_mutexunlock.c b/sched/pthread/pthread_mutexunlock.c
index 6a9bab3f8a..be73134883 100644
--- a/sched/pthread/pthread_mutexunlock.c
+++ b/sched/pthread/pthread_mutexunlock.c
@@ -42,11 +42,45 @@
 #include <unistd.h>
 #include <pthread.h>
 #include <sched.h>
+#include <assert.h>
 #include <errno.h>
 #include <debug.h>
 
 #include "pthread/pthread.h"
 
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: pthread_mutex_unlock
+ *
+ * Description:
+ *   Return true is the mutex is locked.
+ *
+ * Parameters:
+ *   None
+ *
+ * Return Value:
+ *   Returns true if the mutex is locked
+ *
+ ****************************************************************************/
+
+static inline bool pthread_mutex_islocked(FAR struct pthread_mutex_s *mutex)
+{
+  int semcount = mutex->sem.semcount;
+
+  /* The underlying semaphore should have a count less than 2:
+   *
+   *  1 == mutex is unlocked.
+   *  0 == mutex is locked with no waiters
+   * -n == mutex is locked with 'n' waiters.
+   */
+
+  DEBUGASSERT(semcount < 2);
+  return semcount < 1;
+}
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -80,17 +114,27 @@
 
 int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
 {
-  int ret = EINVAL;
+  int ret = OK;
 
   sinfo("mutex=0x%p\n", mutex);
   DEBUGASSERT(mutex != NULL);
+  if (mutex == NULL)
+    {
+      return -EINVAL;
+    }
 
   /* Make sure the semaphore is stable while we make the following checks.
    * This all needs to be one atomic action.
    */
 
   sched_lock();
-  if (mutex != NULL)
+
+  /* The unlock operation is only performed if the mutex is actually locked.
+   * If the mutex is not locked, then SUCCESS will be returned (there is
+   * no error return value specified for this case).
+   */
+
+  if (pthread_mutex_islocked(mutex))
     {
 #if !defined(CONFIG_PTHREAD_MUTEX_UNSAFE) || defined(CONFIG_PTHREAD_MUTEX_TYPES)
       /* Does the calling thread own the semaphore?  If no, should we return