diff --git a/include/cpp2util.h b/include/cpp2util.h
index 57ed3c651..06206def2 100644
--- a/include/cpp2util.h
+++ b/include/cpp2util.h
@@ -1224,14 +1224,14 @@ constexpr auto assert_not_zero(auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAUL
         if constexpr (std::is_signed_v<CPP2_TYPEOF(arg)>) { return std::ssize(x); } \
         else { return std::size(x); } \
     }; \
-    auto msg = "out of bounds access attempt detected - attempted access at index " + std::to_string(arg) + ", "; \
-    if (max() > 0 ) { \
-        msg += "[min,max] range is [0," + std::to_string(max()-1) + "]"; \
-    } \
-    else { \
-        msg += "but container is empty"; \
-    } \
     if (!(0 <= arg && arg < max())) { \
+        auto msg = "out of bounds access attempt detected - attempted access at index " + std::to_string(arg) + ", "; \
+        if (max() > 0 ) { \
+            msg += "[min,max] range is [0," + std::to_string(max()-1) + "]"; \
+        } \
+        else { \
+            msg += "but container is empty"; \
+        } \
         bounds_safety.report_violation(msg.c_str()  CPP2_SOURCE_LOCATION_ARG); \
     } \
     return CPP2_FORWARD(x) [ arg ]; \