diff --git a/src/bake/DevServer/ErrorReportRequest.zig b/src/bake/DevServer/ErrorReportRequest.zig
index a71bfdce6d..766872d841 100644
--- a/src/bake/DevServer/ErrorReportRequest.zig
+++ b/src/bake/DevServer/ErrorReportRequest.zig
@@ -124,9 +124,21 @@ pub fn runWithBody(ctx: *ErrorReportRequest, body: []const u8, r: AnyResponse) !
         }
         const result: *const SourceMapStore.GetResult = &(gop.value_ptr.* orelse continue);
 
-        // When before the first generated line, remap to the HMR runtime
+        // When before the first generated line, remap to the HMR runtime.
+        //
+        // Reminder that the HMR runtime is *not* sourcemapped. And appears
+        // first in the bundle. This means that the mappings usually looks like
+        // this:
+        //
+        // AAAA;;;;;;;;;;;ICGA,qCAA4B;
+        // ^              ^ generated_mappings[1], actual code
+        // ^
+        // ^ generated_mappings[0], we always start it with this
+        //
+        // So we can know if the frame is inside the HMR runtime if
+        // `frame.position.line < generated_mappings[1].lines`.
         const generated_mappings = result.mappings.generated();
-        if (frame.position.line.oneBased() < generated_mappings[1].lines) {
+        if (generated_mappings.len <= 1 or frame.position.line.zeroBased() < generated_mappings[1].lines) {
             frame.source_url = .init(runtime_name); // matches value in source map
             frame.position = .invalid;
             continue;