diff --git a/Sources/AsyncHTTPClient/ConnectionsState.swift b/Sources/AsyncHTTPClient/ConnectionsState.swift
index 9962d5dd5..0c5f908e2 100644
--- a/Sources/AsyncHTTPClient/ConnectionsState.swift
+++ b/Sources/AsyncHTTPClient/ConnectionsState.swift
@@ -229,7 +229,10 @@ extension HTTP1ConnectionProvider {
                 self.openedConnectionsCount -= 1
                 return self.processNextWaiter()
             case .closed:
-                assertionFailure("should not happen")
+                // This can happen in the following scenario: user initiates a connection that will fail to connect,
+                // user calls `syncShutdown` before we received an error from the bootstrap. In this scenario,
+                // pool will be `.closed` but connection will be still in the process of being established/failed,
+                // so then this process finishes, it will get to this point.
                 return .none
             }
         }
diff --git a/Tests/AsyncHTTPClientTests/ConnectionPoolTests+XCTest.swift b/Tests/AsyncHTTPClientTests/ConnectionPoolTests+XCTest.swift
index 0350edf72..b751ec1ce 100644
--- a/Tests/AsyncHTTPClientTests/ConnectionPoolTests+XCTest.swift
+++ b/Tests/AsyncHTTPClientTests/ConnectionPoolTests+XCTest.swift
@@ -34,6 +34,7 @@ extension ConnectionPoolTests {
             ("testAcquireReplace", testAcquireReplace),
             ("testAcquireWhenUnavailableSpecificEL", testAcquireWhenUnavailableSpecificEL),
             ("testAcquireWhenClosed", testAcquireWhenClosed),
+            ("testConnectFailedWhenClosed", testConnectFailedWhenClosed),
             ("testReleaseAliveConnectionEmptyQueue", testReleaseAliveConnectionEmptyQueue),
             ("testReleaseAliveButClosingConnectionEmptyQueue", testReleaseAliveButClosingConnectionEmptyQueue),
             ("testReleaseInactiveConnectionEmptyQueue", testReleaseInactiveConnectionEmptyQueue),
diff --git a/Tests/AsyncHTTPClientTests/ConnectionPoolTests.swift b/Tests/AsyncHTTPClientTests/ConnectionPoolTests.swift
index 0b7f94dee..bacc04dd8 100644
--- a/Tests/AsyncHTTPClientTests/ConnectionPoolTests.swift
+++ b/Tests/AsyncHTTPClientTests/ConnectionPoolTests.swift
@@ -304,9 +304,7 @@ class ConnectionPoolTests: XCTestCase {
 
     func testAcquireWhenClosed() {
         var state = HTTP1ConnectionProvider.ConnectionsState(eventLoop: self.eventLoop)
-        var snapshot = state.testsOnly_getInternalState()
-        snapshot.state = .closed
-        state.testsOnly_setInternalState(snapshot)
+        _ = state.close()
 
         XCTAssertFalse(state.enqueue())
 
@@ -320,6 +318,19 @@ class ConnectionPoolTests: XCTestCase {
         }
     }
 
+    func testConnectFailedWhenClosed() {
+        var state = HTTP1ConnectionProvider.ConnectionsState(eventLoop: self.eventLoop)
+        _ = state.close()
+
+        let action = state.connectFailed()
+        switch action {
+        case .none:
+            break
+        default:
+            XCTFail("Unexpected action: \(action)")
+        }
+    }
+
     // MARK: - Release Tests
 
     func testReleaseAliveConnectionEmptyQueue() throws {
diff --git a/Tests/AsyncHTTPClientTests/HTTPClientInternalTests.swift b/Tests/AsyncHTTPClientTests/HTTPClientInternalTests.swift
index c3cd1241e..5656fbe46 100644
--- a/Tests/AsyncHTTPClientTests/HTTPClientInternalTests.swift
+++ b/Tests/AsyncHTTPClientTests/HTTPClientInternalTests.swift
@@ -797,13 +797,18 @@ class HTTPClientInternalTests: XCTestCase {
     }
 
     func testUncleanCloseThrows() {
-        let httpBin = HTTPBin()
+        let server = NIOHTTP1TestServer(group: self.clientGroup)
         defer {
-            XCTAssertNoThrow(try httpBin.shutdown())
+            XCTAssertNoThrow(try server.stop())
         }
+
         let httpClient = HTTPClient(eventLoopGroupProvider: .shared(self.clientGroup))
 
-        _ = httpClient.get(url: "http://localhost:\(httpBin.port)/wait")
+        _ = httpClient.get(url: "http://localhost:\(server.serverPort)/wait")
+
+        XCTAssertNoThrow(try server.readInbound()) // .head
+        XCTAssertNoThrow(try server.readInbound()) // .end
+
         do {
             try httpClient.syncShutdown(requiresCleanClose: true)
             XCTFail("There should be an error on shutdown")