diff --git a/src/ca/caDiagnostics.h b/src/ca/caDiagnostics.h
index 4956fd82d..850acbc00 100644
--- a/src/ca/caDiagnostics.h
+++ b/src/ca/caDiagnostics.h
@@ -1,4 +1,7 @@
 
+#ifndef caDiagnosticsh
+#define caDiagnosticsh
+
 #include "cadef.h"
 
 #ifdef __cplusplus
@@ -20,4 +23,6 @@ int acctst ( char *pname, unsigned channelCount, unsigned repititionCount,
 
 void caConnTest ( const char *pNameIn, unsigned channelCountIn, double delayIn );
 
+#endif /* caDiagnosticsh */
+