diff --git a/src/grib_accessor_class_local_definition.c b/src/grib_accessor_class_local_definition.c
index 1fa55e09c..a4ea50565 100644
--- a/src/grib_accessor_class_local_definition.c
+++ b/src/grib_accessor_class_local_definition.c
@@ -333,8 +333,14 @@ static int pack_long(grib_accessor* a, const long* val, size_t* len)
             break;
 
         default:
-            grib_context_log(a->context, GRIB_LOG_ERROR, "Invalid localDefinitionNumber %d", localDefinitionNumber);
+#ifdef DEBUG
+            /* In test & development mode, fail so we remember to adjust PDTN */
+            grib_context_log(a->context, GRIB_LOG_ERROR,
+                             "grib_accessor_local_definition: Invalid localDefinitionNumber %d", localDefinitionNumber);
             return GRIB_ENCODING_ERROR;
+#endif
+            /* ECC-1253: Do not fail in operations. Leave PDTN as is */
+            productDefinitionTemplateNumberNew = productDefinitionTemplateNumber;
             break;
     }