diff --git a/util/rundiff b/util/rundiff
index c34bb53a3f..cd2527e543 100755
--- a/util/rundiff
+++ b/util/rundiff
@@ -43,7 +43,7 @@
 #
 
 use strict;
-
+use FileHandle;
 use Getopt::Std;
 
 #
@@ -165,6 +165,8 @@ sub printdiff
 
     # Set $postcontext to print the next $postcontext_lines matching lines.
     $postcontext = $postcontext_lines;
+
+    STDOUT->flush();
 }