diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index 9b3c06fab50b7..076e714d70370 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -514,7 +514,7 @@ fn make_code_region(
         // Extend an empty span by one character so the region will be counted.
         let CharPos(char_pos) = start_col;
         if span.hi() == body_span.hi() {
-            start_col = CharPos(char_pos - 1);
+            start_col = CharPos(char_pos.saturating_sub(1));
         } else {
             end_col = CharPos(char_pos + 1);
         }