diff --git a/src/HttpClient.cpp b/src/HttpClient.cpp
index 31909d9..5344513 100644
--- a/src/HttpClient.cpp
+++ b/src/HttpClient.cpp
@@ -779,7 +779,8 @@ int HttpClient::readHeader()
     case eStatusCodeRead:
         // We're at the start of a line, or somewhere in the middle of reading
         // the Content-Length prefix
-        if (*iContentLengthPtr == c)
+        if ((iTransferEncodingChunkedPtr == kTransferEncodingChunked) &&
+            (tolower((unsigned char)*iContentLengthPtr) == tolower((unsigned char)c)))
         {
             // This character matches, just move along
             iContentLengthPtr++;
@@ -793,7 +794,8 @@ int HttpClient::readHeader()
                 iBodyLengthConsumed = 0;
             }
         }
-        else if (*iTransferEncodingChunkedPtr == c)
+        else if ((iContentLengthPtr == kContentLengthPrefix) &&
+                 (tolower((unsigned char)*iTransferEncodingChunkedPtr) == tolower((unsigned char)c)))
         {
             // This character matches, just move along
             iTransferEncodingChunkedPtr++;
diff --git a/tests/host/Arduino.h b/tests/host/Arduino.h
new file mode 100644
index 0000000..ec89a6b
--- /dev/null
+++ b/tests/host/Arduino.h
@@ -0,0 +1,4 @@
+#pragma once
+#include <ArduinoAPI.h>
+#include <Client.h>
+using namespace arduino;
diff --git a/tests/host/README.md b/tests/host/README.md
new file mode 100644
index 0000000..da860fe
--- /dev/null
+++ b/tests/host/README.md
@@ -0,0 +1,22 @@
+# Response parser regression
+
+Use a local checkout of [ArduinoCore-API](https://github.com/arduino/ArduinoCore-API)
+for the production String/Stream/Client interfaces and its host conversion helpers.
+The test transport supplies in-memory HTTP response bytes; it does not emulate a
+Wi-Fi chip or prove behavior on physical hardware.
+
+From this repository root, set `CORE_API` to that checkout and run:
+
+```sh
+c++ -std=c++11 -fsanitize=address,undefined -Itests/host -I"$CORE_API" \
+  -idirafter "$CORE_API/api" -Isrc src/HttpClient.cpp src/b64.cpp \
+  tests/host/response_headers.cpp "$CORE_API"/api/String.cpp \
+  "$CORE_API"/api/Print.cpp "$CORE_API"/api/Stream.cpp \
+  "$CORE_API"/api/IPAddress.cpp "$CORE_API"/test/src/itoa.cpp \
+  "$CORE_API"/test/src/dtostrf.cpp -o /tmp/http-response-headers
+/tmp/http-response-headers
+```
+
+`-idirafter` avoids shadowing the system `string.h` with Arduino's `String.h`
+on case-insensitive filesystems. The Core API emits existing weak-main warnings
+with Clang on macOS.
diff --git a/tests/host/response_headers.cpp b/tests/host/response_headers.cpp
new file mode 100644
index 0000000..50f8cb2
--- /dev/null
+++ b/tests/host/response_headers.cpp
@@ -0,0 +1,50 @@
+#include "HttpClient.h"
+#include <assert.h>
+#include <stdio.h>
+#include <string>
+
+unsigned long millis() { static unsigned long clock = 0; return ++clock; }
+void delay(unsigned long) {}
+
+class ResponseClient : public Client {
+  std::string response;
+  size_t position = 0;
+public:
+  explicit ResponseClient(const std::string& value) : response(value) {}
+  int connect(IPAddress, uint16_t) override { return 1; }
+  int connect(const char*, uint16_t) override { return 1; }
+  size_t write(uint8_t) override { return 1; }
+  size_t write(const uint8_t*, size_t size) override { return size; }
+  int available() override { return response.size() - position; }
+  int read() override { return available() ? (unsigned char)response[position++] : -1; }
+  int read(uint8_t* data, size_t size) override {
+    size_t count = 0;
+    while (count < size && available()) data[count++] = read();
+    return count;
+  }
+  int peek() override { return available() ? (unsigned char)response[position] : -1; }
+  void flush() override {}
+  void stop() override {}
+  uint8_t connected() override { return available() > 0; }
+  operator bool() override { return true; }
+};
+int main() {
+  for (const char* name : {"Content-Length", "content-length", "CONTENT-LENGTH", "cOnTeNt-LeNgTh"}) {
+    ResponseClient transport(std::string("HTTP/1.1 200 OK\r\nX-Test: ignored\r\n") + name + ": 5\r\n\r\nhello");
+    HttpClient http(transport, "example.test");
+    assert(http.get("/") == 0);
+    assert(http.responseStatusCode() == 200);
+    assert(http.contentLength() == 5);
+    assert(http.responseBody() == "hello");
+  }
+  for (const char* field : {"Transfer-Encoding: chunked", "transfer-encoding: chunked", "TRANSFER-ENCODING: CHUNKED", "tRaNsFeR-EnCoDiNg: ChUnKeD"}) {
+    ResponseClient transport(std::string("HTTP/1.1 200 OK\r\n") + field + "\r\n\r\n5\r\nhello\r\n0\r\n\r\n");
+    HttpClient http(transport, "example.test");
+    assert(http.get("/") == 0);
+    assert(http.responseStatusCode() == 200);
+    assert(http.skipResponseHeaders() == 0);
+    assert(http.isResponseChunked());
+    assert(http.responseBody() == "hello");
+  }
+  puts("eight response-header casing cases passed");
+}