diff --git a/lib/pure/asynchttpserver.nim b/lib/pure/asynchttpserver.nim
index a88a2d2e436fa..6bd9cc9892edf 100644
--- a/lib/pure/asynchttpserver.nim
+++ b/lib/pure/asynchttpserver.nim
@@ -146,15 +146,30 @@ proc respondError(req: Request, code: HttpCode): Future[void] =
   result = req.client.send(msg)
 
 proc parseProtocol(protocol: string): tuple[orig: string, major, minor: int] =
+  template invalidProtocol() =
+    raise newException(ValueError, "Invalid request protocol. Got: " & protocol)
+
   result = default(tuple[orig: string, major, minor: int])
   var i = protocol.skipIgnoreCase("HTTP/")
   if i != 5:
-    raise newException(ValueError, "Invalid request protocol. Got: " &
-        protocol)
+    invalidProtocol()
   result.orig = protocol
-  i.inc protocol.parseSaturatedNatural(result.major, i)
+  let majorLen = protocol.parseSaturatedNatural(result.major, i)
+  if majorLen == 0:
+    invalidProtocol()
+  i.inc majorLen
+
+  if i >= protocol.len or protocol[i] != '.':
+    invalidProtocol()
   i.inc # Skip .
-  i.inc protocol.parseSaturatedNatural(result.minor, i)
+
+  let minorLen = protocol.parseSaturatedNatural(result.minor, i)
+  if minorLen == 0:
+    invalidProtocol()
+  i.inc minorLen
+
+  if i != protocol.len:
+    invalidProtocol()
 
 proc sendStatus(client: AsyncSocket, status: string): Future[void] =
   client.send("HTTP/1.1 " & status & "\c\L\c\L")
diff --git a/tests/stdlib/tasynchttpserver.nim b/tests/stdlib/tasynchttpserver.nim
index 5a7e2da4018a9..3df8b125868c4 100644
--- a/tests/stdlib/tasynchttpserver.nim
+++ b/tests/stdlib/tasynchttpserver.nim
@@ -9,7 +9,7 @@ import strutils
 from net import TimeoutError
 import std/assertions
 
-import httpclient, asynchttpserver, asyncdispatch, asyncfutures
+import httpclient, asynchttpserver, asyncdispatch, asyncfutures, asyncnet
 
 template runTest(
     handler: proc (request: Request): Future[void] {.gcsafe.},
@@ -113,9 +113,39 @@ proc testCustomContentLength() {.async.} =
 
   runTest(handler, request, test)
 
+proc testMalformedProtocolsDoNotCrash() {.async.} =
+  for rawProtocol in [
+    "HTTP/1",
+    "HTTP/.1",
+    "HTTP/1.",
+    "HTTP/1.1xyz",
+  ]:
+    let server = newAsyncHttpServer()
+    server.listen(Port(0))
+
+    var callbackCalled = false
+    proc handler(request: Request) {.async.} =
+      callbackCalled = true
+      await request.respond(Http200, "unexpected")
+
+    asyncCheck server.acceptRequest(handler)
+
+    let client = await asyncnet.dial("127.0.0.1", server.getPort)
+    await client.send("GET / " & rawProtocol & "\c\LHost: localhost\c\L\c\L")
+
+    let lineFut = client.recvLine()
+    doAssert await withTimeout(lineFut, 1000), "Timed out waiting for response to " & rawProtocol
+    doAssert lineFut.read() == "HTTP/1.1 400 Bad Request"
+
+    client.close()
+    await sleepAsync(100)
+    doAssert not callbackCalled
+    server.close()
+
 waitFor(test200())
 waitFor(test404())
 waitFor(testCustomEmptyHeaders())
 waitFor(testCustomContentLength())
+waitFor(testMalformedProtocolsDoNotCrash())
 
 echo "OK"