diff --git a/src/libCom/tsSubr.c b/src/libCom/tsSubr.c
index 80524907f..fa0e2053e 100644
--- a/src/libCom/tsSubr.c
+++ b/src/libCom/tsSubr.c
@@ -119,6 +119,7 @@
 #include <ctype.h>
 #include <string.h>
 #include <limits.h>
+#include <math.h>
 
 #define INC_tsDefs_h
 #if defined(vxWorks)