diff --git a/lib/config-plan9.h b/lib/config-plan9.h
index ce89309bc1..1da74ed85d 100644
--- a/lib/config-plan9.h
+++ b/lib/config-plan9.h
@@ -96,7 +96,6 @@
 #define HAVE_ERRNO_H 1
 #define HAVE_FCNTL 1
 #define HAVE_FCNTL_H 1
-#define HAVE_FDOPEN 1
 #define HAVE_FORK 1
 #define HAVE_FREEADDRINFO 1
 #define HAVE_FTRUNCATE 1
diff --git a/lib/curl_config.h.cmake b/lib/curl_config.h.cmake
index 46b7ef137b..cbbe99b586 100644
--- a/lib/curl_config.h.cmake
+++ b/lib/curl_config.h.cmake
@@ -160,9 +160,6 @@
 /* Define to 1 if you have a working fcntl O_NONBLOCK function. */
 #cmakedefine HAVE_FCNTL_O_NONBLOCK 1
 
-/* Define to 1 if you have the fdopen function. */
-#cmakedefine HAVE_FDOPEN 1
-
 /* Define to 1 if you have the `fork' function. */
 #cmakedefine HAVE_FORK 1