diff --git a/curl.bqn b/curl.bqn
index 4533f00..a2a0963 100644
--- a/curl.bqn
+++ b/curl.bqn
@@ -116,8 +116,8 @@ SetTimeoutms←{timeoutms 𝕊 session:
 # Use a POST method and set data to post
 SetData←{data 𝕊 session:
   "setting up POST request"Check EasySetoptLong⟨session.sessionPtr,curlOptions.post,1⟩
-  "setting POST data"Check EasySetoptStr⟨session.sessionPtr,curlOptions.postfields,data⟩
   "setting POST data size"Check EasySetoptLong⟨session.sessionPtr,curlOptions.postfieldsize,≠data⟩
+  "copying POST data"Check EasySetoptStr⟨session.sessionPtr,curlOptions.copypostfields,data⟩
   session
 }
 
diff --git a/ffi.bqn b/ffi.bqn
index ce3aeae..6d40c46 100644
--- a/ffi.bqn
+++ b/ffi.bqn
@@ -74,6 +74,7 @@ curlOptions←{
   writedata⇐ptrOffset+1  # FILE* in which to write response content
   postfields⇐ptrOffset+15  # pointer to POST input data
   headerdata⇐ptrOffset+29  # FILE* in which to write response headers
+  copypostfields⇐ptrOffset+165 # copy POST input data
 
   # linked list options
   httpHeader⇐slistOffset+23  # HTTP headers as a list of strings
diff --git a/tests.bqn b/tests.bqn
index 73db3fa..b866dd2 100755
--- a/tests.bqn
+++ b/tests.bqn
@@ -36,14 +36,14 @@ simpleAPI_testsuite←⟨
   },
   "simple POST with headers"‿{𝕊𝕩:
     headers←⟨"Content-Type: application/json"⟩
-    r←headers Post ⟨httpbinURL∾"/post","{""key"": ""value""}"⟩
+    r←headers Post ⟨httpbinURL∾"/post",¯1000 + 1000 + "{""key"": 1}"⟩
     ! 200=r.code
     ! 0=r.redirectCount
     ! 1=⊑"HTTP/"⍷r.headers
     ! 1=+´"Content-Type: "⍷r.headers
     ! 1=+´"Content-Length: "⍷r.headers
     ! 1=+´"""Content-Type"": ""application/json"""⍷r.content
-    ! 1=+´"""data"": ""{\""key\"": \""value\""}"""⍷r.content
+    ! 1=+´"""data"": ""{\""key\"": 1}"""⍷ r.content
   }
 ⟩