diff --git a/racket/src/rktio/configure b/racket/src/rktio/configure
index 3b1e598972..5db973338b 100755
--- a/racket/src/rktio/configure
+++ b/racket/src/rktio/configure
@@ -3422,6 +3422,8 @@ case "$host_os" in
     ;;
   *mingw*)
     skip_iconv_check=yes
+    # force pthread off for Windows:
+    enable_pthread=no
     ;;
   cygwin*)
     ;;
diff --git a/racket/src/rktio/configure.ac b/racket/src/rktio/configure.ac
index 5ae225c1d0..288f11036a 100644
--- a/racket/src/rktio/configure.ac
+++ b/racket/src/rktio/configure.ac
@@ -98,7 +98,9 @@ case "$host_os" in
     ;;
   *mingw*)
     skip_iconv_check=yes
-    ;;    
+    # force pthread off for Windows:
+    enable_pthread=no
+    ;;
   cygwin*)
     ;;
   darwin*)