diff --git a/src/os_vms.c b/src/os_vms.c
index 02c594c..84f84ac 100644
--- a/src/os_vms.c
+++ b/src/os_vms.c
@@ -83,7 +83,7 @@
 #define EXPL_ALLOC_INC 64
 
 #define EQN(S1,S2,LN) (strncmp(S1,S2,LN) == 0)
-#define SKIP_FOLLOWING_SLASHES(Str) while (Str[1] == '/') ++Str
+#define SKIP_FOLLOWING_SLASHES(Str) do { while (Str[1] == '/') ++Str; } while (0)
 
 
 /*