diff --git a/src/bun_core/lib.rs b/src/bun_core/lib.rs
index ac446bd1f514..31385a8f5e74 100644
--- a/src/bun_core/lib.rs
+++ b/src/bun_core/lib.rs
@@ -2434,16 +2434,28 @@ pub(crate) mod strings_impl {
             if i >= self.bytes.len() {
                 return false;
             }
-            let b = self.bytes[i];
-            // TODO(port): full UTF-8 decode — bun_str owns the table-driven impl.
-            let (cp, w) = if b < 0x80 {
-                (b as i32, 1u8)
-            } else {
-                (b as i32, 1u8)
-            };
+            let tail = &self.bytes[i..];
+            let b = tail[0];
             cursor.i = i;
-            cursor.c = cp;
-            cursor.width = w;
+            if b < 0x80 {
+                cursor.c = b as i32;
+                cursor.width = 1;
+                return true;
+            }
+            // Multi-byte: defer to the canonical WTF-8 decoder so this stub
+            // stays in lockstep with `strings::CodepointIterator::next`.
+            let len = wtf8_byte_sequence_length(b);
+            let take = (len as usize).min(tail.len());
+            let mut buf = [0u8; 4];
+            buf[..take].copy_from_slice(&tail[..take]);
+            let cp = crate::string::immutable::decode_wtf8_rune_t::<i32>(&buf, len, -1);
+            if cp == -1 {
+                cursor.c = crate::string::immutable::UNICODE_REPLACEMENT as i32;
+                cursor.width = 1;
+            } else {
+                cursor.c = cp;
+                cursor.width = len;
+            }
             true
         }
     }
diff --git a/src/jsc/bindings/wtf-bindings.cpp b/src/jsc/bindings/wtf-bindings.cpp
index c0b6470dac26..14a31372b1ed 100644
--- a/src/jsc/bindings/wtf-bindings.cpp
+++ b/src/jsc/bindings/wtf-bindings.cpp
@@ -14,7 +14,6 @@
 #endif
 
 #if !OS(WINDOWS)
-#include <cassert>
 #include <stdatomic.h>
 
 #include <cassert>
diff --git a/test/bundler/bundler_naming.test.ts b/test/bundler/bundler_naming.test.ts
index e2870b399b3d..678baed2cd62 100644
--- a/test/bundler/bundler_naming.test.ts
+++ b/test/bundler/bundler_naming.test.ts
@@ -302,4 +302,26 @@ describe("bundler", () => {
       },
     ],
   });
+  // A non-ASCII basename char must collapse to a single "_" in the generated
+  // CommonJS wrapper symbol, not one "_" per UTF-8 byte. Regressed to
+  // `require_caf__utils` (the 2 bytes of "é" walked individually) because the
+  // identifier formatter resolved to a stub that never decoded multi-byte
+  // sequences (width always 1).
+  itBundled("naming/NonAsciiSourceFilenameSymbol", {
+    files: {
+      "/entry.js": /* js */ `
+        const u = require("./café-utils.js");
+        console.log(u.hi);
+      `,
+      "/café-utils.js": /* js */ `
+        module.exports = { hi: 1 };
+      `,
+    },
+    target: "bun",
+    onAfterBundle(api) {
+      api.expectFile("/out.js").toContain("require_caf_utils");
+      api.expectFile("/out.js").not.toContain("require_caf__utils");
+    },
+    run: { stdout: "1" },
+  });
 });