diff --git a/kdesrc-build b/kdesrc-build
index 509323a..21a7ceb 100755
--- a/kdesrc-build
+++ b/kdesrc-build
@@ -1597,6 +1597,11 @@ HOME
         # If build-dir starts with a slash, it is an absolute path.
         return $dir if $dir =~ /^\//;
 
+        # Make sure we got a valid option result.
+        if (!$dir) {
+            confess ("Reading option for $subdirOption gave empty \$dir!");
+        }
+
         # If it starts with a tilde, expand it out.
         if ($dir =~ /^~/)
         {