diff --git a/Makefile b/Makefile
index 43c2bbf..85dc5a4 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@
 test: test-heroku-18 test-heroku-16
 
 check:
-	@shellcheck -x bin/compile bin/detect bin/release bin/test-compile bin/utils bin/warnings
+	@shellcheck -x bin/compile bin/detect bin/release bin/test-compile bin/utils bin/warnings bin/default_pythons
 	@shellcheck -x bin/steps/collectstatic bin/steps/eggpath-fix  bin/steps/eggpath-fix2 bin/steps/gdal bin/steps/geo-libs bin/steps/mercurial bin/steps/nltk bin/steps/pip-install bin/steps/pip-uninstall bin/steps/pipenv bin/steps/pipenv-python-version bin/steps/pylibmc bin/steps/python
 	@shellcheck -x bin/steps/hooks/*
 
diff --git a/bin/compile b/bin/compile
index ff01f8b..dfc81d1 100755
--- a/bin/compile
+++ b/bin/compile
@@ -45,16 +45,9 @@ if [[ -n ${BUILDPACK_VENDOR_URL:-} ]]; then
 fi
 export VENDOR_URL
 
-# Which versions of Python are we using?
-# These variables are used to specify which versions of Python to install by default,
-# as well as prompt the user to upgrade if they are using an un–supported version.
-# Note: When 3.7 lands, I recommend switching to LATEST_36 and LATEST_37.
-DEFAULT_PYTHON_VERSION="python-3.6.8"
-LATEST_36="python-3.6.8"
-LATEST_37="python-3.7.2"
-LATEST_35="python-3.5.6"
-LATEST_34="python-3.4.9"
-LATEST_27="python-2.7.15"
+# Default Python Versions
+# shellcheck source=bin/default_pythons
+source "$BIN_DIR/default_pythons"
 
 # Supported Python Branches
 PY37="python-3.7"
@@ -68,8 +61,7 @@ DEFAULT_PYTHON_STACK="cedar-14"
 # If pip doesn't match this version (the version we install), run the installer.
 PIP_UPDATE="9.0.2"
 
-export DEFAULT_PYTHON_VERSION DEFAULT_PYTHON_STACK PIP_UPDATE
-export LATEST_27 LATEST_36 LATEST_37 LATEST_35 LATEST_34
+export DEFAULT_PYTHON_STACK PIP_UPDATE
 export PY37 PY36 PY35 PY27 PY34
 
 # Common Problem Warnings:
diff --git a/bin/default_pythons b/bin/default_pythons
new file mode 100755
index 0000000..7036aae
--- /dev/null
+++ b/bin/default_pythons
@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+
+DEFAULT_PYTHON_VERSION="python-3.6.8"
+LATEST_36="python-3.6.8"
+LATEST_37="python-3.7.2"
+LATEST_35="python-3.5.6"
+LATEST_34="python-3.4.9"
+LATEST_27="python-2.7.16"
+
+export DEFAULT_PYTHON_VERSION LATEST_37 LATEST_36 LATEST_35 LATEST_34 LATEST_27
diff --git a/test/fixtures/python2/runtime.txt b/test/fixtures/python2/runtime.txt
index f27f1cc..d42956d 100644
--- a/test/fixtures/python2/runtime.txt
+++ b/test/fixtures/python2/runtime.txt
@@ -1 +1 @@
-python-2.7.15
+python-2.7.16
diff --git a/test/fixtures/python2_warn/runtime.txt b/test/fixtures/python2_warn/runtime.txt
index 5385682..f27f1cc 100644
--- a/test/fixtures/python2_warn/runtime.txt
+++ b/test/fixtures/python2_warn/runtime.txt
@@ -1 +1 @@
-python-2.7.14
+python-2.7.15
diff --git a/test/run b/test/run
index df9bacb..2bc27cf 100755
--- a/test/run
+++ b/test/run
@@ -1,5 +1,9 @@
 #!/usr/bin/env bash
 
+# Default Python Versions
+# shellcheck source=bin/default_pythons
+source "$BIN_DIR/default_pythons"
+
 testAirflow() {
   export SLUGIFY_USES_TEXT_UNIDECODE="yes"
   compile "airflow"
@@ -19,13 +23,13 @@ testPipenvLock() {
 
 testPipenvVersion() {
   compile "pipenv-version"
-  assertCaptured "3.6.8"
+  assertCaptured $DEFAULT_PYTHON_VERSION
   assertCapturedSuccess
 }
 
 testPipenvVersion2() {
   compile "pipenv-version2"
-  assertCaptured "2.7.15"
+  assertCaptured $LATEST_27
   assertCapturedSuccess
 }
 testPipenvFullVersion() {
@@ -95,25 +99,21 @@ testPylibmc() {
 
 testPythonDefault() {
   compile "pythonDefault"
-  assertCaptured "python-3.6.8"
+  assertCaptured $DEFAULT_PYTHON_VERSION
   assertCapturedSuccess
 }
 
 testPython2() {
     compile "python2"
-    assertCaptured "python-2.7.15"
+    assertCaptured $LATEST_27
     assertCapturedSuccess
 }
 
 testPython2_warn() {
     compile "python2_warn"
-    if [[ $STACK = "heroku-18" ]]; then
-      assertCapturedError
-    else
-      assertCaptured "python-2.7.14"
-      assertCaptured "security update!"
-      assertCapturedSuccess
-    fi
+    assertCaptured "python-2.7.15"
+    assertCaptured "security update!"
+    assertCapturedSuccess
 }
 
 testPython2_fail() {
@@ -124,7 +124,7 @@ testPython2_fail() {
 
 testPython3_4() {
   compile "python3_4"
-  assertCaptured "python-3.4.9"
+  assertCaptured $LATEST_34
   assertCapturedSuccess
 }
 
@@ -147,7 +147,7 @@ testPython3_4_fail() {
 
 testPython3_5() {
   compile "python3_5"
-  assertCaptured "python-3.5.6"
+  assertCaptured $LATEST_35
   assertCapturedSuccess
 }
 
@@ -170,7 +170,7 @@ testPython3_5_fail() {
 
 testPython3_6() {
   compile "python3_6"
-  assertCaptured "python-3.6.8"
+  assertCaptured $LATEST_36
   assertCapturedSuccess
 }
 
@@ -192,7 +192,7 @@ testPython3_7() {
   if [[ $STACK = "cedar-14" ]]; then
     assertCapturedError
   else
-    assertCaptured "python-3.7.2"
+    assertCaptured $LATEST_37
     assertCapturedSuccess
   fi
 }