diff --git a/crates/test_utils/src/fixture.rs b/crates/test_utils/src/fixture.rs
index 535892f3fc..7791460845 100644
--- a/crates/test_utils/src/fixture.rs
+++ b/crates/test_utils/src/fixture.rs
@@ -276,6 +276,7 @@ impl MiniCore {
         }
 
         let mut curr_region = "";
+        let mut seen_regions = Vec::new();
         for line in lines {
             let trimmed = line.trim();
             if let Some(region) = trimmed.strip_prefix("// region:") {
@@ -288,6 +289,7 @@ impl MiniCore {
                 curr_region = "";
                 continue;
             }
+            seen_regions.push(curr_region);
 
             let mut flag = curr_region;
             if let Some(idx) = trimmed.find("// :") {
@@ -305,6 +307,13 @@ impl MiniCore {
                 buf.push_str(line)
             }
         }
+
+        for flag in &self.valid_flags {
+            if !seen_regions.iter().any(|it| it == flag) {
+                panic!("unused minicore flag: {:?}", flag);
+            }
+        }
+
         buf
     }
 }
diff --git a/crates/test_utils/src/minicore.rs b/crates/test_utils/src/minicore.rs
index f9f14b7dfa..8c0d122dc8 100644
--- a/crates/test_utils/src/minicore.rs
+++ b/crates/test_utils/src/minicore.rs
@@ -64,7 +64,7 @@ pub mod ops {
     pub use self::deref::Deref;
     // endregion:deref
 
-    //region:range
+    // region:range
     mod range {
         #[lang = "RangeFull"]
         pub struct RangeFull;
@@ -99,7 +99,7 @@ pub mod ops {
     }
     pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};
     pub use self::range::{RangeInclusive, RangeToInclusive};
-    //endregion:range
+    // endregion:range
 }
 
 // region:slice