diff --git a/src/include/utils/relptr.h b/src/include/utils/relptr.h
index cc80a7200d..c6d39a1360 100644
--- a/src/include/utils/relptr.h
+++ b/src/include/utils/relptr.h
@@ -41,7 +41,7 @@
 #ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
 #define relptr_access(base, rp) \
 	(AssertVariableIsOfTypeMacro(base, char *), \
-	 (__typeof__((rp).relptr_type)) ((rp).relptr_off == 0 ? NULL : \
+	 (__typeof__((rp).relptr_type)) ((rp).relptr_off == ((Size) -1) ? NULL : \
 		(base + (rp).relptr_off)))
 #else
 /*
@@ -50,21 +50,21 @@
  */
 #define relptr_access(base, rp) \
 	(AssertVariableIsOfTypeMacro(base, char *), \
-	 (void *) ((rp).relptr_off == 0 ? NULL : (base + (rp).relptr_off)))
+	 (void *) ((rp).relptr_off == ((Size) -1) ? NULL : (base + (rp).relptr_off)))
 #endif
 
 #define relptr_is_null(rp) \
-	((rp).relptr_off == 0)
+	((rp).relptr_off == ((Size) -1))
 
 /* We use this inline to avoid double eval of "val" in relptr_store */
 static inline Size
 relptr_store_eval(char *base, char *val)
 {
 	if (val == NULL)
-		return 0;
+		return ((Size) -1);
 	else
 	{
-		Assert(val > base);
+		Assert(val >= base);
 		return val - base;
 	}
 }