diff --git a/pkgs/stdenv/darwin/default.nix b/pkgs/stdenv/darwin/default.nix
index 2502882123eb..89c8c6ee2852 100644
--- a/pkgs/stdenv/darwin/default.nix
+++ b/pkgs/stdenv/darwin/default.nix
@@ -50,10 +50,10 @@ rec {
     stripAllFlags=" " # the Darwin "strip" command doesn't know "-s"
     xargsFlags=" "
     export MACOSX_DEPLOYMENT_TARGET=10.7
-    export SDKROOT=
-    export SDKROOT_X=/ # FIXME: impure!
-    export NIX_CFLAGS_COMPILE+=" --sysroot=/var/empty -idirafter $SDKROOT_X/usr/include -F$SDKROOT_X/System/Library/Frameworks -Wno-multichar -Wno-deprecated-declarations"
-    export NIX_LDFLAGS_AFTER+=" -L$SDKROOT_X/usr/lib"
+    # Use the SDK from Xcode by default, falling back to /usr/{lib,include}.
+    export SDKROOT=$(/usr/bin/xcrun --sdk macosx10.9 --show-sdk-path 2> /dev/null || echo /)
+    export NIX_CFLAGS_COMPILE+=" --sysroot=/var/empty -idirafter $SDKROOT/usr/include -F$SDKROOT/System/Library/Frameworks -Wno-multichar -Wno-deprecated-declarations"
+    export NIX_LDFLAGS_AFTER+=" -L$SDKROOT/usr/lib"
     export CMAKE_OSX_ARCHITECTURES=x86_64
   '';