diff --git a/tests/gpgscm/init.scm b/tests/gpgscm/init.scm
index 83261b001..87d3c8870 100644
--- a/tests/gpgscm/init.scm
+++ b/tests/gpgscm/init.scm
@@ -547,11 +547,11 @@
 	(display n)
 	(display ": ")
 	(let ((tag (get-tag f)))
-	  (unless (null? tag)
-		  (display (basename (car tag)))
-		  (display ":")
-		  (display (+ 1 (cdr tag)))
-		  (display ": ")))
+	  (when (and (pair? tag) (string? (car tag)) (number? (cdr tag)))
+		(display (basename (car tag)))
+		(display ":")
+		(display (+ 1 (cdr tag)))
+		(display ": ")))
 	(write f))
 	(newline)
 	(loop (+ n 1) skip (cdr frames))))))
diff --git a/tests/gpgscm/lib.scm b/tests/gpgscm/lib.scm
index 6959aa4d0..2cfe725e9 100644
--- a/tests/gpgscm/lib.scm
+++ b/tests/gpgscm/lib.scm
@@ -20,7 +20,7 @@
 (macro (assert form)
   (let ((tag (get-tag form)))
     `(if (not ,(cadr form))
-	 (throw ,(if (pair? tag)
+	 (throw ,(if (and (pair? tag) (string? (car tag)) (number? (cdr tag)))
 		     `(string-append ,(car tag) ":"
 				     ,(number->string (+ 1 (cdr tag)))
 				     ": Assertion failed: ")