diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -1484,6 +1484,8 @@ size_t SlCalcObjMemberLength(const void 
 	return 0;
 }
 
+#ifdef OTTD_ASSERT
+
 /**
  * Check whether the variable size of the variable in the saveload configuration
  * matches with the actual variable size.
@@ -1524,9 +1526,13 @@ static bool IsVariableSizeRight(const Sa
 	}
 }
 
+#endif /* OTTD_ASSERT */
+
 bool SlObjectMember(void *ptr, const SaveLoad *sld)
 {
+#ifdef OTTD_ASSERT
 	assert(IsVariableSizeRight(sld));
+#endif
 
 	VarType conv = GB(sld->conv, 0, 8);
 	switch (sld->cmd) {