@@ -7,7 +7,7 @@
 """
 import base64
 import json
-from urllib.parse import urlparse
+from urllib.parse import urlencode, urlparse
 
 from . import mitm
 
@@ -84,10 +84,18 @@ def endpoints(path, host):
 
 
 def _body_bytes(post_data):
-    """Bytes of a HAR request postData block (always plain text)."""
+    """Bytes of a HAR request postData block (text, or url-encoded params)."""
     if not post_data:
         return b""
-    return post_data.get("text", "").encode("utf-8")
+    text = post_data.get("text")
+    if text:
+        return text.encode("utf-8")
+    params = post_data.get("params")
+    if params:
+        return urlencode(
+            [(p.get("name", ""), p.get("value", "")) for p in params]
+        ).encode("utf-8")
+    return b""
 
 
 def _content_bytes(content):
 
@@ -62,6 +62,18 @@ def test_from_har_no_auth(tmp_path):
         Session.from_har(str(path), "api.example.com")
 
 
+def test_body_bytes_params_fallback():
+    # HAR form bodies may use postData.params (no text); reconstruct them.
+    pd = {"mimeType": "application/x-www-form-urlencoded",
+          "params": [{"name": "user", "value": "alice"},
+                     {"name": "pw", "value": "s3cret"}]}
+    assert har._body_bytes(pd) == b"user=alice&pw=s3cret"
+    # text still takes precedence, and empty/None still yields b"".
+    assert har._body_bytes({"text": '{"a":1}'}) == b'{"a":1}'
+    assert har._body_bytes(None) == b""
+    assert har._body_bytes({}) == b""
+
+
 def test_base64_response_body():
     eps = har.endpoints(FIXTURE, "api.example.com")
     msg = [e for e in eps if e["path"] == "/v1/messages"][0]