diff --git a/esphome/components/runtime_image/bmp_decoder.h b/esphome/components/runtime_image/bmp_decoder.h
index 73e54f54302..a52a5615849 100644
--- a/esphome/components/runtime_image/bmp_decoder.h
+++ b/esphome/components/runtime_image/bmp_decoder.h
@@ -26,6 +26,10 @@ class BmpDecoder : public ImageDecoder {
   int HOT decode(uint8_t *buffer, size_t size) override;
 
   bool is_finished() const override {
+    if (this->bits_per_pixel_ == 0) {
+      // header not yet received, so dimensions not yet determined
+      return false;
+    }
     // BMP is finished when we've decoded all pixel data
     return this->paint_index_ >= static_cast<size_t>(this->width_ * this->height_);
   }
diff --git a/tests/integration/fixtures/online_image_bmp.yaml b/tests/integration/fixtures/online_image_bmp.yaml
new file mode 100644
index 00000000000..e36514e9ae2
--- /dev/null
+++ b/tests/integration/fixtures/online_image_bmp.yaml
@@ -0,0 +1,27 @@
+esphome:
+  name: online-image-bmp
+
+host:
+
+http_request:
+
+display:
+
+online_image:
+  - url: http://127.0.0.1:HTTP_PORT/foo.bmp
+    id: myimg
+    format: BMP
+    type: RGB
+    on_download_finished:
+      logger.log:
+        format: "download finished. cache hit: %u"
+        args: [cached]
+
+api:
+  actions:
+    - action: fetch_image
+      then:
+        - component.update: myimg
+
+logger:
+  level: DEBUG
diff --git a/tests/integration/test_online_image_bmp.py b/tests/integration/test_online_image_bmp.py
new file mode 100644
index 00000000000..7c32154fdd6
--- /dev/null
+++ b/tests/integration/test_online_image_bmp.py
@@ -0,0 +1,119 @@
+from __future__ import annotations
+
+import asyncio
+import re
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+# black 8x8 RGB BMP, generated with
+#   from PIL import Image
+#   from io import BytesIO
+#   b = BytesIO()
+#   img = Image.new("RGB", (8, 8))
+#   img.save(b, format="BMP")
+#   b.getvalue()
+BMP_IMAGE = b"BM\xf6\x00\x00\x00\x00\x00\x00\x006\x00\x00\x00(\x00\x00\x00\x08\x00\x00\x00\x08\x00\x00\x00\x01\x00\x18\x00\x00\x00\x00\x00\xc0\x00\x00\x00\xc4\x0e\x00\x00\xc4\x0e\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
+LEN_BMP_IMAGE = len(BMP_IMAGE)
+
+
+def handle_http(http_request_future):
+    async def handler(reader, writer):
+        try:
+            async with asyncio.timeout(1.0):
+                data = await reader.readuntil(b"\r\n")
+
+            # ensure our request matches the expectation
+            expected_request = b"GET /foo.bmp HTTP/1.1\r\n"
+            assert data[: len(expected_request)] == expected_request
+
+            # consume rest of request
+            async with asyncio.timeout(1.0):
+                data = await reader.readuntil(b"\r\n\r\n")
+
+            http_request_future.set_result(True)
+
+            http_response = [
+                b"HTTP/1.1 200 OK",
+                b"Content-Length: %d" % LEN_BMP_IMAGE,
+                b"Content-Type: text/plain",
+                b"Connection: close",
+                b"",
+                b"",
+            ]
+            writer.write(b"\r\n".join(http_response))
+            await writer.drain()
+
+            writer.write(BMP_IMAGE)
+
+            await writer.drain()
+        except Exception as exc:
+            if not http_request_future.done():
+                http_request_future.set_exception(exc)
+            raise
+        finally:
+            writer.close()
+
+    return handler
+
+
+@pytest.mark.asyncio
+async def test_online_image_bmp(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Esphome shouldn't block the main loop when a http response is slow"""
+    loop = asyncio.get_running_loop()
+
+    # Track http request
+    http_request_future = loop.create_future()
+    download_finished_future = loop.create_future()
+    downloaded_bytes_future = loop.create_future()
+
+    def check_output(line: str) -> None:
+        """Check log output for expected messages."""
+
+        if match := re.search(r"Image fully downloaded, (\d+) bytes", line):
+            downloaded_bytes_future.set_result(int(match.group(1)))
+
+        if "download finished" in line:
+            download_finished_future.set_result(True)
+
+    server = await asyncio.start_server(
+        handle_http(http_request_future), "127.0.0.1", 0
+    )
+    http_server_port = server.sockets[0].getsockname()[1]
+
+    config = yaml_config.replace("HTTP_PORT", str(http_server_port))
+
+    # Run with log monitoring
+    async with (
+        server,
+        run_compiled(config, line_callback=check_output),
+        api_client_connected() as client,
+    ):
+        # Verify device info
+
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "online-image-bmp"
+
+        # List services to find our test service
+        _, services = await client.list_entities_services()
+
+        # Find test service
+        request_service = next((s for s in services if s.name == "fetch_image"), None)
+
+        assert request_service is not None, "fetch_image service not found"
+
+        await client.execute_service(request_service, {})
+
+        async with asyncio.timeout(0.1):
+            await http_request_future
+
+        async with asyncio.timeout(0.5):
+            numbytes = await downloaded_bytes_future
+            assert numbytes == LEN_BMP_IMAGE
+            await download_finished_future