diff --git a/.github/scripts/install_deps.sh b/.github/scripts/install_deps.sh
index e864e45fa..da984f6a3 100755
--- a/.github/scripts/install_deps.sh
+++ b/.github/scripts/install_deps.sh
@@ -3,9 +3,9 @@
 set -eu
 
 case $# in
-	1) OS="$1"; TOOLSET=    ;;
-	2) OS="$1"; TOOLSET="$2";;
-	*) echo >&2 "Usage: $0 <os> [toolset]" && exit 1;;
+	1) OS="$1"; TOOLSET=     ;;
+	2) OS="$1"; TOOLSET="$2" ;;
+	*) echo >&2 "Usage: $0 <os> [<toolset>]" && exit 1 ;;
 esac
 
 case "${OS%%-*}" in
@@ -21,19 +21,22 @@ case "${OS%%-*}" in
 				TOOLSET=
 			;;
 			'' | lcov)
-				pkgs="$pkgs libpng-dev pkgconf $TOOLSET"
+				pkgs="$pkgs libpng-dev pkgconf python3-pil $TOOLSET"
 				TOOLSET=
 			;;
 		esac
 		sudo apt-get update -qq
 		# shellcheck disable=SC2086 # (This word splitting is intentional.)
 		sudo apt-get install -yq $pkgs
+		case "$TOOLSET" in
+			mingw32|mingw64) py -3 -m pip install pillow ;;
+		esac
 		;;
 	macos)
 		# macOS bundles GNU Make 3.81, which doesn't support synced output.
 		# We leave it as the default in `PATH`, to test that our Makefile works with it.
 		# However, CMake automatically uses Homebrew's `gmake`, so our CI has synced output.
-		brew install bison make
+		brew install bison make pillow
 		# Export `bison` to allow using the version we install from Homebrew,
 		# instead of the outdated one preinstalled on macOS (which doesn't even support `-Wall`...).
 		export PATH="$(brew --prefix)/opt/bison/bin:$PATH"
@@ -47,6 +50,8 @@ case "${OS%%-*}" in
 		choco install -y winflexbison3 cmake
 		# The below expects the base name, not the Windows-specific name.
 		bison() { win_bison "$@"; } # An alias doesn't work, so we use a function instead.
+		# Python and the Pillow library are dependencies for libbet, a repo built by our external tests.
+		py -3 -m pip install pillow
 		;;
 	*)
 		echo "Cannot install deps for OS '$1'"
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 8451017ba..bda28dfcf 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -18,9 +18,6 @@ jobs:
       - name: Install deps
         run: |
           .github/scripts/install_deps.sh ubuntu-latest lcov
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ubuntu
       - name: Generate coverage report
         run: |
           contrib/coverage.bash ubuntu-ci
diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index d77425919..08099e234 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -94,9 +94,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests using our script
         if: matrix.buildsys == 'make'
         run: |
@@ -152,9 +149,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps macos
       - name: Run tests
         run: |
           ctest --test-dir build --schedule-random
@@ -211,9 +205,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests using CTest
         run: |
           ctest --test-dir build --schedule-random -C Debug
@@ -304,9 +295,6 @@ jobs:
         continue-on-error: true
         run: |
           test/fetch-test-deps.sh
-      - name: Install test dependency dependencies
-        run: |
-          test/fetch-test-deps.sh --get-deps ${{ matrix.os }}
       - name: Run tests
         run: |
           test/run-tests.sh --os ${{ matrix.os }}
diff --git a/test/fetch-test-deps.sh b/test/fetch-test-deps.sh
index e27186344..56818bab6 100755
--- a/test/fetch-test-deps.sh
+++ b/test/fetch-test-deps.sh
@@ -10,7 +10,6 @@ Options:
     -h, --help          show this help message
     --only-free         download only freely licensed codebases
     --only-internal     do not download any codebases
-    --get-deps          install programs' own dependencies instead of themselves
     --get-hash          print programs' commit hashes instead of downloading them
     --get-paths         print programs' GitHub paths instead of downloading them
 EOF
@@ -34,11 +33,6 @@ while [[ $# -gt 0 ]]; do
 		--only-internal)
 			external=false
 			;;
-		--get-deps)
-			actionname="$1"
-			shift
-			osname="$1"
-			;;
 		--get-hash|--get-paths)
 			actionname="$1"
 			;;
@@ -54,28 +48,6 @@ while [[ $# -gt 0 ]]; do
 done
 
 case "$actionname" in
-	--get-deps)
-		action() { # _ _ repo _
-			# libbet depends on PIL to build
-			if [ "$3" = "libbet" ]; then
-				case "${osname%%-*}" in
-					ubuntu | debian)
-						sudo apt-get install python3-pil
-						;;
-					macos)
-						python3 -m pip install --break-system-packages pillow
-						;;
-					windows)
-						py -3 -m pip install pillow
-						;;
-					*)
-						echo "WARNING: Cannot install Pillow for OS '$osname'"
-						;;
-				esac
-			fi
-		}
-		;;
-
 	--get-hash)
 		action() { # _ _ repo commit
 			printf "%s@%s-" "$3" "$4"