diff --git a/appveyor.yml b/appveyor.yml
index d3c02ce60..e87600b5a 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -26,7 +26,7 @@ environment:
     CYG_ROOT: C:/cygwin64
     CYG_MIRROR: http://mirrors.kernel.org/sourceware/cygwin/
     CYG_CACHE: C:/cygwin64/var/cache/setup
-    FLEXDLL_VERSION: 0.37
+    FLEXDLL_VERSION: 0.38
     OCAMLRUNPARAM: v=0,b
   matrix:
     - PORT: mingw32
diff --git a/flexdll b/flexdll
index 7f565ef86..b6b231493 160000
--- a/flexdll
+++ b/flexdll
@@ -1 +1 @@
-Subproject commit 7f565ef8647a16e6a2cd2b30c8e6a4894558eaaa
+Subproject commit b6b231493387a7628103dc744b3bcd3d413c80d9
diff --git a/tools/ci/appveyor/appveyor_build.cmd b/tools/ci/appveyor/appveyor_build.cmd
index 5904c9d88..d73807cea 100644
--- a/tools/ci/appveyor/appveyor_build.cmd
+++ b/tools/ci/appveyor/appveyor_build.cmd
@@ -82,8 +82,8 @@ if "%PORT%" equ "mingw32" (
 )
 
 cd "%APPVEYOR_BUILD_FOLDER%"
-appveyor DownloadFile "https://github.com/alainfrisch/flexdll/archive/0.37.tar.gz" -FileName "flexdll.tar.gz" || exit /b 1
-appveyor DownloadFile "https://github.com/alainfrisch/flexdll/releases/download/0.37/flexdll-bin-0.37.zip" -FileName "flexdll.zip" || exit /b 1
+appveyor DownloadFile "https://github.com/alainfrisch/flexdll/archive/%FLEXDLL_VERSION%.tar.gz" -FileName "flexdll.tar.gz" || exit /b 1
+appveyor DownloadFile "https://github.com/alainfrisch/flexdll/releases/download/%FLEXDLL_VERSION%/flexdll-bin-%FLEXDLL_VERSION%.zip" -FileName "flexdll.zip" || exit /b 1
 rem flexdll.zip is processed here, rather than in appveyor_build.sh because the
 rem unzip command comes from MSYS2 (via Git for Windows) and it has to be
 rem invoked via cmd /c in a bash script which is weird(er).