diff --git a/contrib/gitian-build.sh b/contrib/gitian-build.sh
index 52e5ae16e..f5e269f82 100755
--- a/contrib/gitian-build.sh
+++ b/contrib/gitian-build.sh
@@ -184,7 +184,7 @@ then
 fi
 
 # Check for OSX SDK
-if [[ ! -e "gitian-builder/inputs/MacOSX10.11.sdk.tar.gz" && $osx == true ]]
+if [[ ! -e "gitian-builder/inputs/MacOSX10.11.sdk.tar.xz" && $osx == true ]]
 then
     echo "Cannot build for OSX, SDK does not exist. Will build for other OSes"
     osx=false
diff --git a/contrib/gitian-descriptors/gitian-osx.yml b/contrib/gitian-descriptors/gitian-osx.yml
index 1493ec080..6a076b1d2 100644
--- a/contrib/gitian-descriptors/gitian-osx.yml
+++ b/contrib/gitian-descriptors/gitian-osx.yml
@@ -31,7 +31,7 @@ remotes:
 - "url": "https://github.com/floblockchain/flo.git"
   "dir": "flo"
 files:
-- "MacOSX10.11.sdk.tar.gz"
+- "MacOSX10.11.sdk.tar.xz"
 script: |
   WRAP_DIR=$HOME/wrapped
   HOSTS="x86_64-apple-darwin11"
@@ -87,7 +87,7 @@ script: |
   BASEPREFIX=`pwd`/depends
 
   mkdir -p ${BASEPREFIX}/SDKs
-  tar -C ${BASEPREFIX}/SDKs -xf ${BUILD_DIR}/MacOSX10.11.sdk.tar.gz
+  tar -C ${BASEPREFIX}/SDKs -xf ${BUILD_DIR}/MacOSX10.11.sdk.tar.xz
 
   # Build dependencies for each host
   for i in $HOSTS; do
diff --git a/doc/README_osx.md b/doc/README_osx.md
index 148beef8a..d3687ae60 100644
--- a/doc/README_osx.md
+++ b/doc/README_osx.md
@@ -41,7 +41,7 @@ To create a tarball suitable for Gitian input, there are two options:
 Using Mac OS X, you can mount the dmg, and then create it with:
 ```
   $ hdiutil attach Xcode_7.3.1.dmg
-  $ tar -C /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/ -czf MacOSX10.11.sdk.tar.gz MacOSX10.11.sdk
+  $ tar -C /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/ -czf MacOSX10.11.sdk.tar.xz MacOSX10.11.sdk
 ```
 
 Alternatively, you can use 7zip and SleuthKit to extract the files one by one.