diff --git a/src/cas/os/posixRT/osiMutex.h b/src/cas/os/posixRT/osiMutex.h
index 2299cb996..4623a26c5 100644
--- a/src/cas/os/posixRT/osiMutex.h
+++ b/src/cas/os/posixRT/osiMutex.h
@@ -4,7 +4,10 @@
 //
 
 #include <semaphore.h>
+
+#ifndef assert // allow use of epicsAssert.h
 #include <assert.h>
+#endif
 
 class osiMutex {
 public: