diff --git a/ext/pcntl/pcntl.c b/ext/pcntl/pcntl.c
index 54ed5c4b90e91..c1c99ab9a8d85 100644
--- a/ext/pcntl/pcntl.c
+++ b/ext/pcntl/pcntl.c
@@ -1528,9 +1528,11 @@ PHP_FUNCTION(pcntl_rfork)
 		flags |= RFPROC;
 	}
 
+#ifdef RFTSIGZMB
 	if ((flags & RFTSIGZMB) != 0) {
 		flags |= RFTSIGFLAGS(csignal);
 	}
+#endif
 
 	pid = rfork(flags);