diff --git a/include/gtkwave/fstapi.c b/include/gtkwave/fstapi.c
index 91c5401ee..d4adbdc0a 100644
--- a/include/gtkwave/fstapi.c
+++ b/include/gtkwave/fstapi.c
@@ -1646,7 +1646,11 @@ if(1)
                                 {
                                 if(vm4ip[2] != prev_alias)
                                         {
-                                        fpos += fstWriterSVarint(f, (((int64_t)((int32_t)(prev_alias = vm4ip[2]))) << 1) | 1);
+					int32_t  t_i32 = ((int32_t)(prev_alias = vm4ip[2])); /* vm4ip is generic unsigned data */
+					int64_t  t_i64 = (int64_t)t_i32; /* convert to signed */
+					uint64_t t_u64 = (uint64_t)t_i64; /* sign extend through 64b */
+
+					fpos += fstWriterSVarint(f, (int64_t)((t_u64 << 1) | 1)); /* all in this block was: fpos += fstWriterSVarint(f, (((int64_t)((int32_t)(prev_alias = vm4ip[2]))) << 1) | 1); */
                                         }
                                         else
                                         {