diff --git a/CHANGELOG.md b/CHANGELOG.md
index 887e20f..1b212a2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Error if the unsupported `BUILD_WITH_GEO_LIBRARIES` env var is set (#1115).
 - Remove deprecated GDAL/GEOS/PROJ support (#1113).
 - Remove vendored `jq` binary (#1112).
 - Remove redundant Mercurial install step (#1111).
diff --git a/bin/compile b/bin/compile
index 6d48b4d..8bc8094 100755
--- a/bin/compile
+++ b/bin/compile
@@ -35,15 +35,6 @@ ENV_DIR=$3
 # Export Path variables, for use in sub-scripts.
 export BUILD_DIR CACHE_DIR ENV_DIR
 
-if [[ "${STACK}" == "cedar-14" ]]; then
-  puts-warn "The Cedar-14 stack is no longer supported by the latest release of this buildpack."
-  puts-warn "Please switch to the Cedar-14 support branch by using this buildpack URL:"
-  puts-warn "https://github.com/heroku/heroku-buildpack-python#cedar-14"
-  puts-warn "For instructions on how to change the buildpacks used by an app, see:"
-  puts-warn "https://devcenter.heroku.com/articles/buildpacks#setting-a-buildpack-on-an-application"
-  exit 1
-fi
-
 # Set the base URL for downloading buildpack assets like Python runtimes.
 # The user can provide BUILDPACK_S3_BASE_URL to specify a custom target.
 # Note: this is designed for non-Heroku use, as it does not use the user-provided
@@ -105,6 +96,31 @@ source "$BIN_DIR/utils"
 # shellcheck source=bin/warnings
 source "$BIN_DIR/warnings"
 
+if [[ "${STACK}" == "cedar-14" ]]; then
+  mcount "failure.unsupported.cedar-14"
+  puts-warn "The Cedar-14 stack is no longer supported by the latest release of this buildpack."
+  puts-warn
+  puts-warn "Please switch to the Cedar-14 support branch by using this buildpack URL:"
+  puts-warn "https://github.com/heroku/heroku-buildpack-python#cedar-14"
+  puts-warn
+  puts-warn "For instructions on how to change the buildpacks used by an app, see:"
+  puts-warn "https://devcenter.heroku.com/articles/buildpacks#setting-a-buildpack-on-an-application"
+  exit 1
+fi
+
+if [[ -f "${ENV_DIR}/BUILD_WITH_GEO_LIBRARIES" ]]; then
+  mcount "failure.unsupported.BUILD_WITH_GEO_LIBRARIES"
+  puts-warn "The Python buildpack's BUILD_WITH_GEO_LIBRARIES functonality is no longer supported:"
+  puts-warn "https://help.heroku.com/D5INLB1A/python-s-build_with_geo_libraries-legacy-feature-is-now-deprecated"
+  puts-warn
+  puts-warn "For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:"
+  puts-warn "https://github.com/heroku/heroku-geo-buildpack"
+  puts-warn
+  puts-warn "To remove this error message, unset the BUILD_WITH_GEO_LIBRARIES variable using:"
+  puts-warn "heroku config:unset BUILD_WITH_GEO_LIBRARIES"
+  exit 1
+fi
+
 # Make the directory in which we will create symlinks from the temporary build directory
 # to `/app`.
 # Symlinks are required, since Python is not a portable installation.
diff --git a/bin/warnings b/bin/warnings
index 034d0dd..a97b076 100755
--- a/bin/warnings
+++ b/bin/warnings
@@ -46,21 +46,7 @@ six-included() {
   fi
 }
 
-geo-gdal-support() {
-  if [[ -f "${ENV_DIR}/BUILD_WITH_GEO_LIBRARIES" ]]; then
-    mcount "warnings.BUILD_WITH_GEO_LIBRARIES"
-    echo
-    puts-warn "The Python buildpack's BUILD_WITH_GEO_LIBRARIES functonality is no longer supported:"
-    puts-warn "https://help.heroku.com/D5INLB1A/python-s-build_with_geo_libraries-legacy-feature-is-now-deprecated"
-    puts-warn
-    puts-warn "For GDAL, GEOS and PROJ support, use the Geo buildpack alongside the Python buildpack:"
-    puts-warn "https://github.com/heroku/heroku-geo-buildpack"
-    puts-warn
-    puts-warn "To hide this message, unset the BUILD_WITH_GEO_LIBRARIES variable using:"
-    puts-warn "heroku config:unset BUILD_WITH_GEO_LIBRARIES"
-    echo
-    return
-  fi
+gdal-missing() {
   if grep -qi 'Could not find gdal-config' "$WARNINGS_LOG"; then
     mcount 'warnings.gdal'
     echo
@@ -76,6 +62,6 @@ show-warnings() {
   scipy-included
   distribute-included
   six-included
-  geo-gdal-support
+  gdal-missing
 }