diff --git a/ghost/admin/package.json b/ghost/admin/package.json
index 67ee6da52e..cde337933a 100644
--- a/ghost/admin/package.json
+++ b/ghost/admin/package.json
@@ -65,7 +65,7 @@
     "ember-cli-mirage": "1.1.6",
     "ember-cli-moment-shim": "3.7.1",
     "ember-cli-node-assets": "0.2.2",
-    "ember-cli-postcss": "5.0.0",
+    "ember-cli-postcss": "6.0.0",
     "ember-cli-shims": "1.2.0",
     "ember-cli-string-helpers": "4.0.6",
     "ember-cli-test-loader": "3.0.0",
diff --git a/ghost/admin/yarn.lock b/ghost/admin/yarn.lock
index 091e8d285b..668b0d96aa 100644
--- a/ghost/admin/yarn.lock
+++ b/ghost/admin/yarn.lock
@@ -2992,7 +2992,7 @@ broccoli-funnel@2.0.1:
     symlink-or-copy "^1.0.0"
     walk-sync "^0.3.1"
 
-broccoli-funnel@3.0.2:
+broccoli-funnel@3.0.2, broccoli-funnel@^3.0.0:
   version "3.0.2"
   resolved "https://registry.yarnpkg.com/broccoli-funnel/-/broccoli-funnel-3.0.2.tgz#25e1c9a512b3852d3c9dde19ebdf07880d619c73"
   integrity sha512-yRa7f0H/BtfqXNmL4eCYtAiVAQASI5b83//17MxAYp3I+w8XzGY8Tc3mwhdUrAgh6Zhb6LZwgvUZDZPTLmkK7w==
@@ -3068,7 +3068,7 @@ broccoli-lint-eslint@^5.0.0:
     lodash.defaultsdeep "^4.6.0"
     md5-hex "^2.0.0"
 
-broccoli-merge-trees@4.1.0, broccoli-merge-trees@^4.1.0:
+broccoli-merge-trees@4.1.0, broccoli-merge-trees@^4.0.0, broccoli-merge-trees@^4.1.0:
   version "4.1.0"
   resolved "https://registry.yarnpkg.com/broccoli-merge-trees/-/broccoli-merge-trees-4.1.0.tgz#a30e2e4c5bb0f5eb8981e8af33a8077714c11f1a"
   integrity sha512-1OXsksKPFiRdiZZOfh1z1mm7ZqKezlMS+DPBpHMDLSb6AhYHvoQfjf0KuMXbY8aoYskj7+Z+EJ5SsS/OC2v5yw==
@@ -3232,24 +3232,26 @@ broccoli-plugin@^4.0.1:
     rimraf "^3.0.0"
     symlink-or-copy "^1.3.0"
 
-broccoli-postcss-single@^3.0.0:
-  version "3.0.0"
-  resolved "https://registry.yarnpkg.com/broccoli-postcss-single/-/broccoli-postcss-single-3.0.0.tgz#1393f87b69e4bbf20a1a1e614e09bbf066db28a2"
-  integrity sha512-+CsV6zdK9CXTplZvQeAsZm7mEh+BwIN6GBzpqm7agqsMZTvW6kkcWDaL2ahG1+Aq2HfLYk1Sam6iQ3jdESNmPA==
+broccoli-postcss-single@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/broccoli-postcss-single/-/broccoli-postcss-single-4.0.0.tgz#221d995cc526e99e5e55feb5613ac57767033fbb"
+  integrity sha512-cs1DWTMnrS1FiKNtJ9vsHhTUHRD++4D+n0p8S/xLmAHJCifZyOMeJfiLJeh61hT+dCgeNrhaBERyNWuCG5hfrg==
   dependencies:
     broccoli-caching-writer "^3.0.3"
     include-path-searcher "^0.1.0"
-    mkdirp "^0.5.1"
+    minimist ">=1.2.5"
+    mkdirp "^1.0.3"
     object-assign "^4.1.1"
     postcss "^7.0.0"
 
-broccoli-postcss@^5.0.0:
-  version "5.0.0"
-  resolved "https://registry.yarnpkg.com/broccoli-postcss/-/broccoli-postcss-5.0.0.tgz#b4ac48e936b0ce0032e68a5872d54323fcf4744d"
-  integrity sha512-iJk+meVt0Oe33iaaE0T6z2lxSs349BRD7pz2kk/I6MuSjjWrZSzP/2txmEHQN7LyQGZjbC222MzBgSQj/O8kTw==
+broccoli-postcss@^5.1.0:
+  version "5.1.0"
+  resolved "https://registry.yarnpkg.com/broccoli-postcss/-/broccoli-postcss-5.1.0.tgz#5b660fa72ba921b01574b4ab10449b20890bba0a"
+  integrity sha512-f5cHP5g7EFidu9w88WOLTtbk4dd/W7amK0nek08FkmUII2h4W/Je4EV26HtMEm9nb1hKI301wwuEQ5AQRsVYog==
   dependencies:
-    broccoli-funnel "^2.0.1"
+    broccoli-funnel "^3.0.0"
     broccoli-persistent-filter "^2.1.0"
+    minimist ">=1.2.5"
     object-assign "^4.1.1"
     postcss "^7.0.5"
 
@@ -5369,15 +5371,15 @@ ember-cli-path-utils@^1.0.0:
   resolved "https://registry.yarnpkg.com/ember-cli-path-utils/-/ember-cli-path-utils-1.0.0.tgz#4e39af8b55301cddc5017739b77a804fba2071ed"
   integrity sha1-Tjmvi1UwHN3FAXc5t3qAT7ogce0=
 
-ember-cli-postcss@5.0.0:
-  version "5.0.0"
-  resolved "https://registry.yarnpkg.com/ember-cli-postcss/-/ember-cli-postcss-5.0.0.tgz#07891b2950e0a6e8b35234d5960575d0471da50a"
-  integrity sha512-znJOyXeYmhDF3DOocfcCUrnGN0iWmDGvMJKTVPszFeBd1/cqx+lSxc1Tx25RAF1KpOyI0FqD1amp6s9lud62EQ==
+ember-cli-postcss@6.0.0:
+  version "6.0.0"
+  resolved "https://registry.yarnpkg.com/ember-cli-postcss/-/ember-cli-postcss-6.0.0.tgz#b5545d9998fe201b39e3df20cf520997095ec9db"
+  integrity sha512-4yVcO9QWDtW8Hassd+Vg5TYCuCJHYgSDuHrgZlBNG0mffZgzWV5PzeAs2n/SnvZOxPfkFegGZHci0/8IX2ctvA==
   dependencies:
     broccoli-file-creator "^2.1.1"
-    broccoli-merge-trees "^3.0.0"
-    broccoli-postcss "^5.0.0"
-    broccoli-postcss-single "^3.0.0"
+    broccoli-merge-trees "^4.0.0"
+    broccoli-postcss "^5.1.0"
+    broccoli-postcss-single "^4.0.0"
     ember-cli-babel "^7.1.0"
     merge "^1.2.0"
 
@@ -9618,7 +9620,7 @@ minimist@1.2.0:
   resolved "https://registry.yarnpkg.com/minimist/-/minimist-1.2.0.tgz#a35008b20f41383eec1fb914f4cd5df79a264284"
   integrity sha1-o1AIsg9BOD7sH7kU9M1d95omQoQ=
 
-minimist@^1.1.1, minimist@^1.1.3, minimist@^1.2.0:
+minimist@>=1.2.5, minimist@^1.1.1, minimist@^1.1.3, minimist@^1.2.0:
   version "1.2.5"
   resolved "https://registry.yarnpkg.com/minimist/-/minimist-1.2.5.tgz#67d66014b66a6a8aaa0c083c5fd58df4e4e97602"
   integrity sha512-FM9nNUYrRBAELZQT3xeZQ7fmMOBg6nWNmJKTcgsJeaLstP/UODVpGsr5OhXhhXg6f+qtJ8uiZ+PUxkDWcgIXLw==
@@ -9704,7 +9706,7 @@ mkdirp@0.5.1, mkdirp@^0.5.0, mkdirp@^0.5.1, mkdirp@~0.5.0, mkdirp@~0.5.1:
   dependencies:
     minimist "0.0.8"
 
-mkdirp@~1.0.3:
+mkdirp@^1.0.3, mkdirp@~1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-1.0.3.tgz#4cf2e30ad45959dddea53ad97d518b6c8205e1ea"
   integrity sha512-6uCP4Qc0sWsgMLy1EOqqS/3rjDHOEnsStVr/4vtAIK2Y5i2kA7lFFejYrpIyiN9w0pYf4ckeCYT9f1r1P9KX5g==