diff --git a/std/textproto/mod.ts b/std/textproto/mod.ts
index 06ffb73640..218ec9d442 100644
--- a/std/textproto/mod.ts
+++ b/std/textproto/mod.ts
@@ -74,22 +74,16 @@ export class TextProtoReader {
       if (kv === Deno.EOF) throw new Deno.errors.UnexpectedEof();
       if (kv.byteLength === 0) return m;
 
-      // Key ends at first colon; should not have trailing spaces
-      // but they appear in the wild, violating specs, so we remove
-      // them if present.
+      // Key ends at first colon
       let i = kv.indexOf(charCode(":"));
       if (i < 0) {
         throw new Deno.errors.InvalidData(
           `malformed MIME header line: ${str(kv)}`
         );
       }
-      let endKey = i;
-      while (endKey > 0 && kv[endKey - 1] == charCode(" ")) {
-        endKey--;
-      }
 
       //let key = canonicalMIMEHeaderKey(kv.subarray(0, endKey));
-      const key = str(kv.subarray(0, endKey));
+      const key = str(kv.subarray(0, i));
 
       // As per RFC 7230 field-name is a token,
       // tokens consist of one or more chars.
diff --git a/std/textproto/test.ts b/std/textproto/test.ts
index 5833935baa..b9947ab33a 100644
--- a/std/textproto/test.ts
+++ b/std/textproto/test.ts
@@ -94,7 +94,7 @@ test({
   },
 });
 
-// Test that we read slightly-bogus MIME headers seen in the wild,
+// Test that we don't read MIME headers seen in the wild,
 // with spaces before colons, and spaces in keys.
 test({
   name: "[textproto] Reader : MIME Header Non compliant",
@@ -109,9 +109,10 @@ test({
     const m = assertNotEOF(await r.readMIMEHeader());
     assertEquals(m.get("Foo"), "bar");
     assertEquals(m.get("Content-Language"), "en");
-    assertEquals(m.get("SID"), "0");
-    assertEquals(m.get("Privilege"), "127");
-    // Not a legal http header
+    // Make sure we drop headers with trailing whitespace
+    assertEquals(m.get("SID"), null);
+    assertEquals(m.get("Privilege"), null);
+    // Not legal http header
     assertThrows((): void => {
       assertEquals(m.get("Audio Mode"), "None");
     });