diff -up mutt-1.5.21/mutt_ssl_gnutls.c.testcert mutt-1.5.21/mutt_ssl_gnutls.c
--- mutt-1.5.21/mutt_ssl_gnutls.c.testcert	2010-08-25 18:31:40.000000000 +0200
+++ mutt-1.5.21/mutt_ssl_gnutls.c	2013-11-04 14:15:33.956762683 +0100
@@ -434,8 +434,16 @@ static int tls_compare_certificates (con
       return 0;
     }
 
-    ptr = (unsigned char *)strstr((char*)b64_data.data, CERT_SEP) + 1;
-    ptr = (unsigned char *)strstr((char*)ptr, CERT_SEP);
+    /* find start of cert, skipping junk */
+    ptr = (unsigned char *)strstr((char*)b64_data.data, CERT_SEP);
+    if (!ptr)
+    {
+      gnutls_free(cert.data);
+      FREE (&b64_data_data);
+      return 0;
+    }
+    /* find start of next cert */
+    ptr = (unsigned char *)strstr((char*)ptr + 1, CERT_SEP);
 
     b64_data.size = b64_data.size - (ptr - b64_data.data);
     b64_data.data = ptr;