diff --git a/lib/replace/system/time.h b/lib/replace/system/time.h
index b6d26092890..00f0d7f99e6 100644
--- a/lib/replace/system/time.h
+++ b/lib/replace/system/time.h
@@ -79,13 +79,21 @@ int rep_utimes(const char *filename, const struct timeval tv[2]);
 typedef int clockid_t;
 int rep_clock_gettime(clockid_t clk_id, struct timespec *tp);
 #endif
-/* make sure we have a best effort CUSTOM_CLOCK_MONOTONIC we can rely on */
+/* make sure we have a best effort CUSTOM_CLOCK_MONOTONIC we can rely on.
+ *
+ * on AIX the values of CLOCK_* are cast expressions, not integer constants,
+ * this prevents them from being compared against in a preprocessor directive.
+ * The following ...IS_* macros can be used to check which clock is in use.
+ */
 #if defined(CLOCK_MONOTONIC)
 #define CUSTOM_CLOCK_MONOTONIC CLOCK_MONOTONIC
+#define CUSTOM_CLOCK_MONOTONIC_IS_MONOTONIC
 #elif defined(CLOCK_HIGHRES)
 #define CUSTOM_CLOCK_MONOTONIC CLOCK_HIGHRES
+#define CUSTOM_CLOCK_MONOTONIC_IS_HIGHRES
 #else
 #define CUSTOM_CLOCK_MONOTONIC CLOCK_REALTIME
+#define CUSTOM_CLOCK_MONOTONIC_IS_REALTIME
 #endif
 
 #endif
diff --git a/lib/util/time.c b/lib/util/time.c
index 8c01627e2a1..8a4d93d4ac1 100644
--- a/lib/util/time.c
+++ b/lib/util/time.c
@@ -60,7 +60,7 @@ _PUBLIC_ void clock_gettime_mono(struct timespec *tp)
 	}
 #endif
 /* then try the  monotonic clock: */
-#if CUSTOM_CLOCK_MONOTONIC != CLOCK_REALTIME
+#ifndef CUSTOM_CLOCK_MONOTONIC_IS_REALTIME
 	if (clock_gettime(CUSTOM_CLOCK_MONOTONIC,tp) == 0) {
 		return;
 	}