diff --git a/akka-http-core/src/main/scala/akka/http/engine/parsing/SpecializedHeaderValueParsers.scala b/akka-http-core/src/main/scala/akka/http/engine/parsing/SpecializedHeaderValueParsers.scala
index 35f90d6228..d5a56189f6 100644
--- a/akka-http-core/src/main/scala/akka/http/engine/parsing/SpecializedHeaderValueParsers.scala
+++ b/akka-http-core/src/main/scala/akka/http/engine/parsing/SpecializedHeaderValueParsers.scala
@@ -7,7 +7,7 @@ package akka.http.engine.parsing
 import scala.annotation.tailrec
 import akka.util.ByteString
 import akka.http.model.{ HttpHeader, ErrorInfo }
-import akka.http.model.headers.`Content-Length`
+import akka.http.model.headers.{ RawHeader, `Content-Length` }
 import akka.http.model.parser.CharacterClasses._
 
 /**
@@ -22,9 +22,10 @@ private object SpecializedHeaderValueParsers {
     def apply(input: ByteString, valueStart: Int, warnOnIllegalHeader: ErrorInfo ⇒ Unit): (HttpHeader, Int) = {
       @tailrec def recurse(ix: Int = valueStart, result: Long = 0): (HttpHeader, Int) = {
         val c = byteChar(input, ix)
-        if (DIGIT(c) && result >= 0) recurse(ix + 1, result * 10 + c - '0')
+        if (result < 0) fail("`Content-Length` header value must not exceed 63-bit integer range")
+        else if (DIGIT(c)) recurse(ix + 1, result * 10 + c - '0')
         else if (WSP(c)) recurse(ix + 1, result)
-        else if (c == '\r' && byteChar(input, ix + 1) == '\n' && result >= 0) (`Content-Length`(result), ix + 2)
+        else if (c == '\r' && byteChar(input, ix + 1) == '\n') (`Content-Length`(result), ix + 2)
         else fail("Illegal `Content-Length` header value")
       }
       recurse()
diff --git a/akka-http-core/src/test/scala/akka/http/engine/parsing/ContentLengthHeaderParserSpec.scala b/akka-http-core/src/test/scala/akka/http/engine/parsing/ContentLengthHeaderParserSpec.scala
index 349896d2c0..7b54ff0d7b 100644
--- a/akka-http-core/src/test/scala/akka/http/engine/parsing/ContentLengthHeaderParserSpec.scala
+++ b/akka-http-core/src/test/scala/akka/http/engine/parsing/ContentLengthHeaderParserSpec.scala
@@ -13,14 +13,14 @@ class ContentLengthHeaderParserSpec extends WordSpec with Matchers {
 
   "specialized ContentLength parser" should {
     "accept zero" in {
-      parse("0") === 0L
+      parse("0") shouldEqual 0L
     }
     "accept positive value" in {
-      parse("43234398") === 43234398L
+      parse("43234398") shouldEqual 43234398L
     }
     "accept positive value > Int.MaxValue <= Long.MaxValue" in {
-      parse("274877906944") === 274877906944L
-      parse("9223372036854775807") === 9223372036854775807L // Long.MaxValue
+      parse("274877906944") shouldEqual 274877906944L
+      parse("9223372036854775807") shouldEqual 9223372036854775807L // Long.MaxValue
     }
     "don't accept positive value > Long.MaxValue" in {
       a[ParsingException] should be thrownBy parse("9223372036854775808") // Long.MaxValue + 1
diff --git a/akka-http-core/src/test/scala/akka/http/engine/parsing/RequestParserSpec.scala b/akka-http-core/src/test/scala/akka/http/engine/parsing/RequestParserSpec.scala
index 707389913a..92b7d3a3bd 100644
--- a/akka-http-core/src/test/scala/akka/http/engine/parsing/RequestParserSpec.scala
+++ b/akka-http-core/src/test/scala/akka/http/engine/parsing/RequestParserSpec.scala
@@ -349,7 +349,7 @@ class RequestParserSpec extends FreeSpec with Matchers with BeforeAndAfterAll {
             |Content-length: 92233720368547758080
             |Host: x
             |
-            |""" should parseToError(400: StatusCode, ErrorInfo("Illegal `Content-Length` header value"))
+            |""" should parseToError(400: StatusCode, ErrorInfo("`Content-Length` header value must not exceed 63-bit integer range"))
         }
       }
     }