diff --git a/src/igc.c b/src/igc.c
index 9882a08208e..e2240a2d9f7 100644
--- a/src/igc.c
+++ b/src/igc.c
@@ -1559,8 +1559,11 @@ fix_native_cu (mps_ss_t ss, struct Lisp_Native_Comp_Unit *u)
   MPS_SCAN_BEGIN (ss)
   {
     IGC_FIX_CALL_FN (ss, struct Lisp_Vector, u, fix_vectorlike);
-    size_t n = ASIZE (u->data_impure_vec);
-    IGC_FIX12_NOBJS (ss, u->data_imp_relocs, n);
+    if (u->data_imp_relocs)
+      {
+	size_t n = ASIZE (u->data_impure_vec);
+	IGC_FIX12_NOBJS (ss, u->data_imp_relocs, n);
+      }
   }
   MPS_SCAN_END (ss);
   return MPS_RES_OK;