Index: cackey.c
==================================================================
--- cackey.c
+++ cackey.c
@@ -5180,10 +5180,18 @@
 			return(sign_ret);
 		}
 
 		CACKEY_DEBUG_PRINTF("Error.  SignFinal() returned failure (rv = %lu).", (unsigned long) sign_ret);
 
+		return(sign_ret);
+	}
+
+	if (pSignature == NULL) {
+		CACKEY_DEBUG_PRINTF("pSignature specified as NULL, undoing C_SignUpdate()", (unsigned long) sign_ret);
+
+		cackey_sessions[hSession].sign_bufused = start_sign_bufused;
+
 		return(sign_ret);
 	}
 
 	CACKEY_DEBUG_PRINTF("Returning CKR_OK (%i)", CKR_OK);