diff --git a/Sources/GRPC/GRPCServerPipelineConfigurator.swift b/Sources/GRPC/GRPCServerPipelineConfigurator.swift
index 5854faea9..61155426b 100644
--- a/Sources/GRPC/GRPCServerPipelineConfigurator.swift
+++ b/Sources/GRPC/GRPCServerPipelineConfigurator.swift
@@ -33,8 +33,8 @@ final class GRPCServerPipelineConfigurator: ChannelInboundHandler, RemovableChan
   /// The server configuration.
   private let configuration: Server.Configuration
 
-  /// Reads which we're holding on to before the pipeline is configured.
-  private var bufferedReads = CircularBuffer<NIOAny>()
+  /// A buffer containing the buffered bytes.
+  private var buffer: ByteBuffer?
 
   /// The current state.
   private var state: State
@@ -212,13 +212,17 @@ final class GRPCServerPipelineConfigurator: ChannelInboundHandler, RemovableChan
     buffer: ByteBuffer,
     context: ChannelHandlerContext
   ) {
-    if HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer) {
+    switch HTTPVersionParser.determineHTTPVersion(buffer) {
+    case .http2:
       self.configureHTTP2(context: context)
-    } else if HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer) {
+    case .http1:
       self.configureHTTP1(context: context)
-    } else {
+    case .unknown:
+      // Neither H2 nor H1 or the length limit has been exceeded.
       self.configuration.logger.error("Unable to determine http version, closing")
       context.close(mode: .all, promise: nil)
+    case .notEnoughBytes:
+      () // Try again with more bytes.
     }
   }
 
@@ -268,13 +272,9 @@ final class GRPCServerPipelineConfigurator: ChannelInboundHandler, RemovableChan
 
   /// Try to parse the buffered data to determine whether or not HTTP/2 or HTTP/1 should be used.
   private func tryParsingBufferedData(context: ChannelHandlerContext) {
-    guard let first = self.bufferedReads.first else {
-      // No data buffered yet. We'll try when we read.
-      return
+    if let buffer = self.buffer {
+      self.determineHTTPVersionAndConfigurePipeline(buffer: buffer, context: context)
     }
-
-    let buffer = self.unwrapInboundIn(first)
-    self.determineHTTPVersionAndConfigurePipeline(buffer: buffer, context: context)
   }
 
   // MARK: - Channel Handler
@@ -312,7 +312,8 @@ final class GRPCServerPipelineConfigurator: ChannelInboundHandler, RemovableChan
   }
 
   internal func channelRead(context: ChannelHandlerContext, data: NIOAny) {
-    self.bufferedReads.append(data)
+    var buffer = self.unwrapInboundIn(data)
+    self.buffer.setOrWriteBuffer(&buffer)
 
     switch self.state {
     case .notConfigured(alpn: .notExpected),
@@ -335,8 +336,9 @@ final class GRPCServerPipelineConfigurator: ChannelInboundHandler, RemovableChan
     removalToken: ChannelHandlerContext.RemovalToken
   ) {
     // Forward any buffered reads.
-    while let read = self.bufferedReads.popFirst() {
-      context.fireChannelRead(read)
+    if let buffer = self.buffer {
+      self.buffer = nil
+      context.fireChannelRead(self.wrapInboundOut(buffer))
     }
     context.leavePipeline(removalToken: removalToken)
   }
@@ -375,16 +377,64 @@ struct HTTPVersionParser {
 
   /// Determines whether the bytes in the `ByteBuffer` are prefixed with the HTTP/2 client
   /// connection preface.
-  static func prefixedWithHTTP2ConnectionPreface(_ buffer: ByteBuffer) -> Bool {
+  static func prefixedWithHTTP2ConnectionPreface(_ buffer: ByteBuffer) -> SubParseResult {
     let view = buffer.readableBytesView
 
     guard view.count >= HTTPVersionParser.http2ClientMagic.count else {
       // Not enough bytes.
-      return false
+      return .notEnoughBytes
     }
 
     let slice = view[view.startIndex ..< view.startIndex.advanced(by: self.http2ClientMagic.count)]
-    return slice.elementsEqual(HTTPVersionParser.http2ClientMagic)
+    return slice.elementsEqual(HTTPVersionParser.http2ClientMagic) ? .accepted : .rejected
+  }
+
+  enum ParseResult: Hashable {
+    case http1
+    case http2
+    case unknown
+    case notEnoughBytes
+  }
+
+  enum SubParseResult: Hashable {
+    case accepted
+    case rejected
+    case notEnoughBytes
+  }
+
+  private static let maxLengthToCheck = 1024
+
+  static func determineHTTPVersion(_ buffer: ByteBuffer) -> ParseResult {
+    switch Self.prefixedWithHTTP2ConnectionPreface(buffer) {
+    case .accepted:
+      return .http2
+
+    case .notEnoughBytes:
+      switch Self.prefixedWithHTTP1RequestLine(buffer) {
+      case .accepted:
+        // Not enough bytes to check H2, but enough to confirm H1.
+        return .http1
+      case .notEnoughBytes:
+        // Not enough bytes to check H2 or H1.
+        return .notEnoughBytes
+      case .rejected:
+        // Not enough bytes to check H2 and definitely not H1.
+        return .notEnoughBytes
+      }
+
+    case .rejected:
+      switch Self.prefixedWithHTTP1RequestLine(buffer) {
+      case .accepted:
+        // Not H2, but H1 is confirmed.
+        return .http1
+      case .notEnoughBytes:
+        // Not H2, but not enough bytes to reject H1 yet.
+        return .notEnoughBytes
+      case .rejected:
+        // Not H2 or H1.
+        return .unknown
+      }
+    }
   }
 
   private static let http1_1 = [
@@ -399,29 +449,59 @@ struct HTTPVersionParser {
   ]
 
   /// Determines whether the bytes in the `ByteBuffer` are prefixed with an HTTP/1.1 request line.
-  static func prefixedWithHTTP1RequestLine(_ buffer: ByteBuffer) -> Bool {
+  static func prefixedWithHTTP1RequestLine(_ buffer: ByteBuffer) -> SubParseResult {
     var readableBytesView = buffer.readableBytesView
 
+    // We don't need to validate the request line, only determine whether we think it's an HTTP1
+    // request line. Another handler will parse it properly.
+
     // From RFC 2616 § 5.1:
     //   Request-Line = Method SP Request-URI SP HTTP-Version CRLF
 
-    // Read off the Method and Request-URI (and spaces).
-    guard readableBytesView.trimPrefix(to: UInt8(ascii: " ")) != nil,
-          readableBytesView.trimPrefix(to: UInt8(ascii: " ")) != nil else {
-      return false
+    // Get through the first space.
+    guard readableBytesView.dropPrefix(through: UInt8(ascii: " ")) != nil else {
+      let tooLong = buffer.readableBytes > Self.maxLengthToCheck
+      return tooLong ? .rejected : .notEnoughBytes
+    }
+
+    // Get through the second space.
+    guard readableBytesView.dropPrefix(through: UInt8(ascii: " ")) != nil else {
+      let tooLong = buffer.readableBytes > Self.maxLengthToCheck
+      return tooLong ? .rejected : .notEnoughBytes
+    }
+
+    // +2 for \r\n
+    guard readableBytesView.count >= (Self.http1_1.count + 2) else {
+      return .notEnoughBytes
     }
 
-    // Read off the HTTP-Version and CR.
-    guard let versionView = readableBytesView.trimPrefix(to: UInt8(ascii: "\r")) else {
-      return false
+    guard let version = readableBytesView.dropPrefix(through: UInt8(ascii: "\r")),
+          readableBytesView.first == UInt8(ascii: "\n") else {
+      // If we didn't drop the prefix OR we did and the next byte wasn't '\n', then we had enough
+      // bytes but the '\r\n' wasn't present: reject this as being HTTP1.
+      return .rejected
+    }
+
+    return version.elementsEqual(Self.http1_1) ? .accepted : .rejected
+  }
+}
+
+extension Collection where Self == Self.SubSequence, Self.Element: Equatable {
+  /// Drops the prefix off the collection up to and including the first `separator`
+  /// only if that separator appears in the collection.
+  ///
+  /// Returns the prefix up to but not including the separator if it was found, nil otherwise.
+  mutating func dropPrefix(through separator: Element) -> SubSequence? {
+    if self.isEmpty {
+      return nil
     }
 
-    // Check that the LF followed the CR.
-    guard readableBytesView.first == UInt8(ascii: "\n") else {
-      return false
+    guard let separatorIndex = self.firstIndex(of: separator) else {
+      return nil
     }
 
-    // Now check the HTTP version.
-    return versionView.elementsEqual(HTTPVersionParser.http1_1)
+    let prefix = self[..<separatorIndex]
+    self = self[self.index(after: separatorIndex)...]
+    return prefix
   }
 }
diff --git a/Tests/GRPCTests/GRPCServerPipelineConfiguratorTests.swift b/Tests/GRPCTests/GRPCServerPipelineConfiguratorTests.swift
index 173f2e5a9..59da4837f 100644
--- a/Tests/GRPCTests/GRPCServerPipelineConfiguratorTests.swift
+++ b/Tests/GRPCTests/GRPCServerPipelineConfiguratorTests.swift
@@ -135,6 +135,24 @@ class GRPCServerPipelineConfiguratorTests: GRPCTestCase {
     self.assertHTTP2Handler(isPresent: true)
   }
 
+  func testHTTP2SetupViaBytesDripFed() {
+    self.setUp(tls: false)
+    var bytes = ByteBuffer(staticString: "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")
+    var head = bytes.readSlice(length: bytes.readableBytes - 1)!
+    let tail = bytes.readSlice(length: 1)!
+
+    while let slice = head.readSlice(length: 1) {
+      assertThat(try self.channel.writeInbound(slice), .doesNotThrow())
+      self.assertConfigurator(isPresent: true)
+      self.assertHTTP2Handler(isPresent: false)
+    }
+
+    // Final byte.
+    assertThat(try self.channel.writeInbound(tail), .doesNotThrow())
+    self.assertConfigurator(isPresent: false)
+    self.assertHTTP2Handler(isPresent: true)
+  }
+
   func testHTTP1Dot1SetupViaBytes() {
     self.setUp(tls: false)
     let bytes = ByteBuffer(staticString: "GET http://www.foo.bar HTTP/1.1\r\n")
@@ -143,6 +161,39 @@ class GRPCServerPipelineConfiguratorTests: GRPCTestCase {
     self.assertGRPCWebToHTTP2Handler(isPresent: true)
   }
 
+  func testHTTP1Dot1SetupViaBytesDripFed() {
+    self.setUp(tls: false)
+    var bytes = ByteBuffer(staticString: "GET http://www.foo.bar HTTP/1.1\r\n")
+    var head = bytes.readSlice(length: bytes.readableBytes - 1)!
+    let tail = bytes.readSlice(length: 1)!
+
+    while let slice = head.readSlice(length: 1) {
+      assertThat(try self.channel.writeInbound(slice), .doesNotThrow())
+      self.assertConfigurator(isPresent: true)
+      self.assertGRPCWebToHTTP2Handler(isPresent: false)
+    }
+
+    // Final byte.
+    assertThat(try self.channel.writeInbound(tail), .doesNotThrow())
+    self.assertConfigurator(isPresent: false)
+    self.assertGRPCWebToHTTP2Handler(isPresent: true)
+  }
+
+  func testUnexpectedInputClosesEventuallyWhenDripFed() {
+    self.setUp(tls: false)
+    var bytes = ByteBuffer(repeating: UInt8(ascii: "a"), count: 2048)
+
+    while let slice = bytes.readSlice(length: 1) {
+      assertThat(try self.channel.writeInbound(slice), .doesNotThrow())
+      self.assertConfigurator(isPresent: true)
+      self.assertHTTP2Handler(isPresent: false)
+      self.assertGRPCWebToHTTP2Handler(isPresent: false)
+    }
+
+    self.channel.embeddedEventLoop.run()
+    assertThat(try self.channel.closeFuture.wait(), .doesNotThrow())
+  }
+
   func testReadsAreUnbufferedAfterConfiguration() throws {
     self.setUp(tls: false)
 
diff --git a/Tests/GRPCTests/HTTPVersionParserTests.swift b/Tests/GRPCTests/HTTPVersionParserTests.swift
index ff866408c..2dc36979d 100644
--- a/Tests/GRPCTests/HTTPVersionParserTests.swift
+++ b/Tests/GRPCTests/HTTPVersionParserTests.swift
@@ -22,58 +22,64 @@ class HTTPVersionParserTests: GRPCTestCase {
 
   func testHTTP2ExactlyTheRightBytes() {
     let buffer = ByteBuffer(string: self.preface)
-    XCTAssertTrue(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer), .accepted)
   }
 
   func testHTTP2TheRightBytesAndMore() {
     var buffer = ByteBuffer(string: self.preface)
     buffer.writeRepeatingByte(42, count: 1024)
-    XCTAssertTrue(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer), .accepted)
   }
 
   func testHTTP2NoBytes() {
     let empty = ByteBuffer()
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(empty))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(empty), .notEnoughBytes)
   }
 
   func testHTTP2NotEnoughBytes() {
     var buffer = ByteBuffer(string: self.preface)
     buffer.moveWriterIndex(to: buffer.writerIndex - 1)
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer), .notEnoughBytes)
   }
 
   func testHTTP2EnoughOfTheWrongBytes() {
     let buffer = ByteBuffer(string: String(self.preface.reversed()))
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer), .rejected)
   }
 
   func testHTTP1RequestLine() {
     let buffer = ByteBuffer(staticString: "GET https://grpc.io/index.html HTTP/1.1\r\n")
-    XCTAssertTrue(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .accepted)
   }
 
   func testHTTP1RequestLineAndMore() {
     let buffer = ByteBuffer(staticString: "GET https://grpc.io/index.html HTTP/1.1\r\nMore")
-    XCTAssertTrue(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .accepted)
   }
 
   func testHTTP1RequestLineWithoutCRLF() {
     let buffer = ByteBuffer(staticString: "GET https://grpc.io/index.html HTTP/1.1")
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .notEnoughBytes)
   }
 
   func testHTTP1NoBytes() {
     let empty = ByteBuffer()
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP1RequestLine(empty))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(empty), .notEnoughBytes)
   }
 
   func testHTTP1IncompleteRequestLine() {
     let buffer = ByteBuffer(staticString: "GET https://grpc.io/index.html")
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .notEnoughBytes)
   }
 
   func testHTTP1MalformedVersion() {
     let buffer = ByteBuffer(staticString: "GET https://grpc.io/index.html ptth/1.1\r\n")
-    XCTAssertFalse(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer))
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .rejected)
+  }
+
+  func testTooManyIncorrectBytes() {
+    let buffer = ByteBuffer(repeating: UInt8(ascii: "\r"), count: 2048)
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP2ConnectionPreface(buffer), .rejected)
+    XCTAssertEqual(HTTPVersionParser.prefixedWithHTTP1RequestLine(buffer), .rejected)
   }
 }