diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 767f8e9f4fa15..ed0e104d6b6a0 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -427,6 +427,12 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
                 let merged_prefix_len = self.curr_original_span.lo() - self.curr().span.lo();
                 let after_macro_bang =
                     merged_prefix_len + BytePos(visible_macro.as_str().len() as u32 + 1);
+                if self.curr().span.lo() + after_macro_bang > self.curr().span.hi() {
+                    // Something is wrong with the macro name span;
+                    // return now to avoid emitting malformed mappings.
+                    // FIXME(#117788): Track down why this happens.
+                    return;
+                }
                 let mut macro_name_cov = self.curr().clone();
                 self.curr_mut().span =
                     self.curr().span.with_lo(self.curr().span.lo() + after_macro_bang);