diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala
index 690a81627e..361288c970 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala
@@ -55,10 +55,23 @@ private[http] object HttpServerBluePrint {
       }.withDeploy(Deploy.local)
     }, errorMsg = "Http.serverLayer is currently not reusable. You need to create a new instance for each materialization.")
 
+    def establishAbsoluteUri(requestOutput: RequestOutput): RequestOutput = requestOutput match {
+      case start: RequestStart ⇒
+        try {
+          val effectiveUri = HttpRequest.effectiveUri(start.uri, start.headers, securedConnection = false, defaultHostHeader)
+          start.copy(uri = effectiveUri)
+        } catch {
+          case e: IllegalUriException ⇒
+            MessageStartError(StatusCodes.BadRequest, ErrorInfo("Request is missing required `Host` header", e.getMessage))
+        }
+      case x ⇒ x
+    }
+
     val requestParsingFlow = Flow[ByteString].transform(() ⇒
       // each connection uses a single (private) request parser instance for all its requests
       // which builds a cache of all header instances seen on that connection
       rootParser.createShallowCopy(() ⇒ oneHundredContinueRef).stage).named("rootParser")
+      .map(establishAbsoluteUri)
 
     val requestPreparation =
       Flow[RequestOutput]
@@ -66,14 +79,13 @@ private[http] object HttpServerBluePrint {
         .via(headAndTailFlow)
         .map {
           case (RequestStart(method, uri, protocol, hdrs, createEntity, _, _), entityParts) ⇒
-            val effectiveUri = HttpRequest.effectiveUri(uri, hdrs, securedConnection = false, defaultHostHeader)
             val effectiveMethod = if (method == HttpMethods.HEAD && transparentHeadRequests) HttpMethods.GET else method
             val effectiveHeaders =
               if (settings.remoteAddressHeader && remoteAddress.isDefined)
                 headers.`Remote-Address`(RemoteAddress(remoteAddress.get)) +: hdrs
               else hdrs
 
-            HttpRequest(effectiveMethod, effectiveUri, effectiveHeaders, createEntity(entityParts), protocol)
+            HttpRequest(effectiveMethod, uri, effectiveHeaders, createEntity(entityParts), protocol)
           case (_, src) ⇒ src.runWith(Sink.ignore)
         }.collect {
           case r: HttpRequest ⇒ r
diff --git a/akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerSpec.scala b/akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerSpec.scala
index 9cae0f8c68..51a08a6323 100644
--- a/akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerSpec.scala
+++ b/akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerSpec.scala
@@ -661,6 +661,32 @@ class HttpServerSpec extends AkkaSpec("akka.loggers = []\n akka.loglevel = OFF")
       expectRequest shouldEqual HttpRequest(uri = "http://example.com//foo", headers = List(Host("example.com")))
     }
 
+    "use default-host-header for HTTP/1.0 requests" in new TestSetup {
+      send("""GET /abc HTTP/1.0
+             |
+             |""".stripMarginWithNewline("\r\n"))
+
+      expectRequest shouldEqual HttpRequest(uri = "http://example.com/abc", protocol = HttpProtocols.`HTTP/1.0`)
+
+      override def settings: ServerSettings = super.settings.copy(defaultHostHeader = Host("example.com"))
+    }
+    "fail an HTTP/1.0 request with 400 if no default-host-header is set" in new TestSetup {
+      send("""GET /abc HTTP/1.0
+             |
+             |""".stripMarginWithNewline("\r\n"))
+
+      netOutSub.request(1)
+      wipeDate(netOut.expectNext().utf8String) shouldEqual
+        """|HTTP/1.1 400 Bad Request
+           |Server: akka-http/test
+           |Date: XXXX
+           |Connection: close
+           |Content-Type: text/plain; charset=UTF-8
+           |Content-Length: 41
+           |
+           |Request is missing required `Host` header""".stripMarginWithNewline("\r\n")
+    }
+
     "support remote-address-header" in new TestSetup {
       lazy val theAddress = InetAddress.getByName("127.5.2.1")