diff --git a/src/libCom/osi/os/RTEMS/osiUnistd.h b/src/libCom/osi/os/RTEMS/osiUnistd.h
index 87da50649..9e9dab38b 100644
--- a/src/libCom/osi/os/RTEMS/osiUnistd.h
+++ b/src/libCom/osi/os/RTEMS/osiUnistd.h
@@ -39,6 +39,11 @@ extern "C" {
 int putenv (char *);
 char *strdup (const char *);
 
+int snprintf(char *str, size_t size, const char *format, ...);
+#include <stdarg.h>
+int vsnprintf(char *str, size_t size, const char *format, va_list ap);
+
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/libCom/osi/os/posix/epicsStdio.cpp b/src/libCom/osi/os/posix/epicsStdio.cpp
index 0933b4f4f..e575563ab 100644
--- a/src/libCom/osi/os/posix/epicsStdio.cpp
+++ b/src/libCom/osi/os/posix/epicsStdio.cpp
@@ -9,6 +9,7 @@
 \*************************************************************************/
 
 #include <epicsStdio.h>
+#include <osiUnistd.h>
 
 extern "C" {