diff --git a/frontend/dockerfile/docs/rules/legacy-key-value-format.md b/frontend/dockerfile/docs/rules/legacy-key-value-format.md
index 32003b399c57..3008e3fb4878 100644
--- a/frontend/dockerfile/docs/rules/legacy-key-value-format.md
+++ b/frontend/dockerfile/docs/rules/legacy-key-value-format.md
@@ -36,3 +36,21 @@ FROM alpine
 ARG foo=bar
 ```
 
+❌ Bad: multi-line variable declaration with a space separator.
+
+```dockerfile
+ENV DEPS \
+    curl \
+    git \
+    make
+```
+
+✅ Good: use an equals sign and wrap the value in quotes.
+
+```dockerfile
+ENV DEPS="\
+    curl \
+    git \
+    make"
+```
+
diff --git a/frontend/dockerfile/linter/docs/LegacyKeyValueFormat.md b/frontend/dockerfile/linter/docs/LegacyKeyValueFormat.md
index ccf8450bfe78..b54f3d8ea9dd 100644
--- a/frontend/dockerfile/linter/docs/LegacyKeyValueFormat.md
+++ b/frontend/dockerfile/linter/docs/LegacyKeyValueFormat.md
@@ -28,3 +28,21 @@ ARG foo bar
 FROM alpine
 ARG foo=bar
 ```
+
+❌ Bad: multi-line variable declaration with a space separator.
+
+```dockerfile
+ENV DEPS \
+    curl \
+    git \
+    make
+```
+
+✅ Good: use an equals sign and wrap the value in quotes.
+
+```dockerfile
+ENV DEPS="\
+    curl \
+    git \
+    make"
+```