diff --git a/debug.js b/debug.js
index 98cab11..14bd9fe 100644
--- a/debug.js
+++ b/debug.js
@@ -126,7 +126,7 @@ debug.enabled = function(name) {
  */
 
 function coerce(val) {
-  if (val instanceof Error) return val.stack;
+  if (val instanceof Error) return val.stack || val.message;
   return val;
 }
 
diff --git a/lib/debug.js b/lib/debug.js
index 8e2b841..3b0a918 100644
--- a/lib/debug.js
+++ b/lib/debug.js
@@ -142,6 +142,6 @@ function debug(name) {
  */
 
 function coerce(val) {
-  if (val instanceof Error) return val.stack;
+  if (val instanceof Error) return val.stack || val.message;
   return val;
 }