diff --git a/2.3/alpine3.7/Dockerfile b/2.3/alpine3.7/Dockerfile
index 12c841b101..2853a4ce53 100644
--- a/2.3/alpine3.7/Dockerfile
+++ b/2.3/alpine3.7/Dockerfile
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.3/jessie/Dockerfile b/2.3/jessie/Dockerfile
index eace3b8c49..8a12e622b7 100644
--- a/2.3/jessie/Dockerfile
+++ b/2.3/jessie/Dockerfile
@@ -66,12 +66,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.3/jessie/slim/Dockerfile b/2.3/jessie/slim/Dockerfile
index 0de9a637c9..70939abf84 100644
--- a/2.3/jessie/slim/Dockerfile
+++ b/2.3/jessie/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.3/stretch/Dockerfile b/2.3/stretch/Dockerfile
index ee6c536ce9..0f75c01fd7 100644
--- a/2.3/stretch/Dockerfile
+++ b/2.3/stretch/Dockerfile
@@ -68,12 +68,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.3/stretch/slim/Dockerfile b/2.3/stretch/slim/Dockerfile
index 3dbfc7f760..2b4e438c2b 100644
--- a/2.3/stretch/slim/Dockerfile
+++ b/2.3/stretch/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/alpine3.6/Dockerfile b/2.4/alpine3.6/Dockerfile
index d6071461e9..d6dc0462a6 100644
--- a/2.4/alpine3.6/Dockerfile
+++ b/2.4/alpine3.6/Dockerfile
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/alpine3.7/Dockerfile b/2.4/alpine3.7/Dockerfile
index 8bf6723afb..4b0dd8205a 100644
--- a/2.4/alpine3.7/Dockerfile
+++ b/2.4/alpine3.7/Dockerfile
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/jessie/Dockerfile b/2.4/jessie/Dockerfile
index 591d088a31..de82348f3b 100644
--- a/2.4/jessie/Dockerfile
+++ b/2.4/jessie/Dockerfile
@@ -66,12 +66,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/jessie/slim/Dockerfile b/2.4/jessie/slim/Dockerfile
index 190c973ec2..92842cc513 100644
--- a/2.4/jessie/slim/Dockerfile
+++ b/2.4/jessie/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/stretch/Dockerfile b/2.4/stretch/Dockerfile
index cc08911031..34899060d2 100644
--- a/2.4/stretch/Dockerfile
+++ b/2.4/stretch/Dockerfile
@@ -66,12 +66,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.4/stretch/slim/Dockerfile b/2.4/stretch/slim/Dockerfile
index ac2b07fd0f..a2d97467de 100644
--- a/2.4/stretch/slim/Dockerfile
+++ b/2.4/stretch/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.5/alpine3.7/Dockerfile b/2.5/alpine3.7/Dockerfile
index 71725f3db4..d80296285d 100644
--- a/2.5/alpine3.7/Dockerfile
+++ b/2.5/alpine3.7/Dockerfile
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.5/stretch/Dockerfile b/2.5/stretch/Dockerfile
index c654d97eba..14d8198af1 100644
--- a/2.5/stretch/Dockerfile
+++ b/2.5/stretch/Dockerfile
@@ -66,12 +66,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.5/stretch/slim/Dockerfile b/2.5/stretch/slim/Dockerfile
index c80c031db7..8a71a2e25b 100644
--- a/2.5/stretch/slim/Dockerfile
+++ b/2.5/stretch/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.6-rc/alpine3.7/Dockerfile b/2.6-rc/alpine3.7/Dockerfile
index 42e029b4de..a3f9ada1c6 100644
--- a/2.6-rc/alpine3.7/Dockerfile
+++ b/2.6-rc/alpine3.7/Dockerfile
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.6-rc/stretch/Dockerfile b/2.6-rc/stretch/Dockerfile
index 34c2178b4f..6ba905b7c5 100644
--- a/2.6-rc/stretch/Dockerfile
+++ b/2.6-rc/stretch/Dockerfile
@@ -66,12 +66,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/2.6-rc/stretch/slim/Dockerfile b/2.6-rc/stretch/slim/Dockerfile
index 26af3b352c..e687be268f 100644
--- a/2.6-rc/stretch/slim/Dockerfile
+++ b/2.6-rc/stretch/slim/Dockerfile
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/Dockerfile-alpine.template b/Dockerfile-alpine.template
index 1d0f9e0ef5..4a75626e5f 100644
--- a/Dockerfile-alpine.template
+++ b/Dockerfile-alpine.template
@@ -101,12 +101,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/Dockerfile-debian.template b/Dockerfile-debian.template
index ee05fcc0b0..3eb568b968 100644
--- a/Dockerfile-debian.template
+++ b/Dockerfile-debian.template
@@ -68,12 +68,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]
diff --git a/Dockerfile-slim.template b/Dockerfile-slim.template
index 8b0038c72e..3c2846a417 100644
--- a/Dockerfile-slim.template
+++ b/Dockerfile-slim.template
@@ -92,12 +92,12 @@ RUN set -ex \
 # and don't create ".bundle" in all our apps
 ENV GEM_HOME /usr/local/bundle
 ENV BUNDLE_PATH="$GEM_HOME" \
-	BUNDLE_BIN="$GEM_HOME/bin" \
 	BUNDLE_SILENCE_ROOT_WARNING=1 \
 	BUNDLE_APP_CONFIG="$GEM_HOME"
 # path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
-ENV PATH $BUNDLE_PATH/gems/bin:$PATH
-RUN mkdir -p "$GEM_HOME" "$BUNDLE_BIN" \
-	&& chmod 777 "$GEM_HOME" "$BUNDLE_BIN"
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
 
 CMD [ "irb" ]