diff --git a/sigrok.h b/sigrok.h
index 4b6e2640..8b2e1265 100644
--- a/sigrok.h
+++ b/sigrok.h
@@ -50,9 +50,9 @@
 #define SIGROK_ERR_SAMPLERATE		-3 /* Incorrect samplerate */
 
 /* Handy little macros */
-#define KHZ(n) (n * 1000)
-#define MHZ(n) (n * 1000000)
-#define GHZ(n) (n * 1000000000)
+#define KHZ(n) ((n) * 1000)
+#define MHZ(n) ((n) * 1000000)
+#define GHZ(n) ((n) * 1000000000)
 
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))