diff --git a/lib/internal/webidl.js b/lib/internal/webidl.js
index 36bde94013d1a8..85bfb2c3db3180 100644
--- a/lib/internal/webidl.js
+++ b/lib/internal/webidl.js
@@ -108,11 +108,14 @@ function pow2(exponent) {
 
 // https://tc39.es/ecma262/#eqn-modulo
 // The notation “x modulo y” computes a value k of the same sign as y.
+// As y is always positive in this file, we can do a simple r < 0 check for that.
 function modulo(x, y) {
   const r = x % y;
   // Convert -0 to +0.
   if (r === 0) {
     return 0;
+  } else if (r < 0) {
+    return r + y;
   }
   return r;
 }
diff --git a/test/parallel/test-internal-webidl-converttoint.js b/test/parallel/test-internal-webidl-converttoint.js
index 7e7c024387a0ec..8260d9d8d29914 100644
--- a/test/parallel/test-internal-webidl-converttoint.js
+++ b/test/parallel/test-internal-webidl-converttoint.js
@@ -56,3 +56,12 @@ assert.strictEqual(convertToInt('x', 0xFFFF_FFFF, 32), 0xFFFF_FFFF);
 // Out of range, step 11.
 assert.strictEqual(convertToInt('x', 0x8000_0000, 32, { signed: true }), -0x8000_0000);
 assert.strictEqual(convertToInt('x', 0xFFF_FFFF, 32, { signed: true }), 0xFFF_FFFF);
+
+// Negative values must wrap as two's-complement, matching typed-array behavior.
+assert.strictEqual(convertToInt('x', -3, 8), 253);
+assert.strictEqual(convertToInt('x', -3, 8), new Uint8Array([-3])[0]);
+assert.strictEqual(convertToInt('x', -1, 32), 0xFFFF_FFFF);
+assert.strictEqual(convertToInt('x', -1, 32), new Uint32Array([-1])[0]);
+assert.strictEqual(convertToInt('x', -200, 8, { signed: true }), 56);
+assert.strictEqual(convertToInt('x', -200, 8, { signed: true }),
+                   new Int8Array([-200])[0]);