diff --git a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsCodec.java b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsCodec.java
index 52db1ce..1ffb7e2 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsCodec.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsCodec.java
@@ -48,6 +48,7 @@
     codedOut.writeBoolNoTag(semantics.incompatibleDisallowDictPlus());
     codedOut.writeBoolNoTag(semantics.incompatibleDisallowKeywordOnlyArgs());
     codedOut.writeBoolNoTag(semantics.incompatibleDisallowToplevelIfStatement());
+    codedOut.writeBoolNoTag(semantics.incompatibleDisallowUncalledSetConstructor());
     codedOut.writeBoolNoTag(semantics.incompatibleListPlusEqualsInplace());
     codedOut.writeBoolNoTag(semantics.incompatibleLoadArgumentIsLabel());
     codedOut.writeBoolNoTag(semantics.incompatibleNewActionsApi());
@@ -70,6 +71,7 @@
     builder.incompatibleDisallowDictPlus(codedIn.readBool());
     builder.incompatibleDisallowKeywordOnlyArgs(codedIn.readBool());
     builder.incompatibleDisallowToplevelIfStatement(codedIn.readBool());
+    builder.incompatibleDisallowUncalledSetConstructor(codedIn.readBool());
     builder.incompatibleListPlusEqualsInplace(codedIn.readBool());
     builder.incompatibleLoadArgumentIsLabel(codedIn.readBool());
     builder.incompatibleNewActionsApi(codedIn.readBool());
diff --git a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
index 0f8e0c4..6545d06 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
@@ -159,6 +159,17 @@
   public boolean incompatibleDisallowToplevelIfStatement;
 
   @Option(
+    name = "incompatible_disallow_uncalled_set_constructor",
+    defaultValue = "false",
+    category = "incompatible changes",
+    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+    effectTags = {OptionEffectTag.UNKNOWN},
+    metadataTags = {OptionMetadataTag.INCOMPATIBLE_CHANGE},
+    help = "If set to true, it's not allowed to use `set()` even if that code is never executed."
+  )
+  public boolean incompatibleDisallowUncalledSetConstructor;
+
+  @Option(
     name = "incompatible_list_plus_equals_inplace",
     defaultValue = "true",
     category = "incompatible changes",
@@ -244,6 +255,7 @@
         .incompatibleDisallowDictPlus(incompatibleDisallowDictPlus)
         .incompatibleDisallowKeywordOnlyArgs(incompatibleDisallowKeywordOnlyArgs)
         .incompatibleDisallowToplevelIfStatement(incompatibleDisallowToplevelIfStatement)
+        .incompatibleDisallowUncalledSetConstructor(incompatibleDisallowUncalledSetConstructor)
         .incompatibleListPlusEqualsInplace(incompatibleListPlusEqualsInplace)
         .incompatibleLoadArgumentIsLabel(incompatibleLoadArgumentIsLabel)
         .incompatibleNewActionsApi(incompatibleNewActionsApi)
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java b/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
index a60ec53..110c9e1 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/BazelLibrary.java
@@ -175,36 +175,6 @@
   }
 
   @SkylarkSignature(
-    name = "set",
-    returnType = SkylarkNestedSet.class,
-    doc =
-        "A temporary alias for <a href=\"#depset\">depset</a>. "
-            + "Deprecated in favor of <code>depset</code>.",
-    parameters = {
-      @Param(
-        name = "items",
-        type = Object.class,
-        defaultValue = "[]",
-        doc = "Same as for <a href=\"#depset\">depset</a>."
-      ),
-      @Param(
-        name = "order",
-        type = String.class,
-        defaultValue = "\"default\"",
-        doc = "Same as for <a href=\"#depset\">depset</a>."
-      )
-    },
-    useLocation = true
-  )
-  private static final BuiltinFunction set =
-      new BuiltinFunction("set") {
-        public SkylarkNestedSet invoke(Object items, String order, Location loc)
-            throws EvalException {
-          throw new EvalException(loc, "The function 'set' has been removed in favor of 'depset'.");
-        }
-      };
-
-  @SkylarkSignature(
     name = "union",
     objectType = SkylarkNestedSet.class,
     returnType = SkylarkNestedSet.class,
@@ -285,7 +255,7 @@
       };
 
   private static Environment.Frame createGlobals() {
-    List<BaseFunction> bazelGlobalFunctions = ImmutableList.of(select, depset, set, type);
+    List<BaseFunction> bazelGlobalFunctions = ImmutableList.of(select, depset, type);
 
     try (Mutability mutability = Mutability.create("BUILD")) {
       Environment env = Environment.builder(mutability)
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java b/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java
index a0dc773..1bbf78c 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Identifier.java
@@ -94,6 +94,13 @@
     if (name.equals("$error$")) {
       return new EvalException(getLocation(), "contains syntax error(s)", true);
     }
+    if (name.equals("set")) {
+      //TODO(vladmos): Remove as soon as the flag is removed
+      return new EvalException(getLocation(),
+          "The function 'set' has been removed in favor of 'depset', please use the latter. "
+              + "You can temporarily refer to the old 'set' constructor from unexecuted code "
+              + "by using --incompatible_disallow_uncalled_set_constructor=false");
+    }
     String suggestion = SpellChecker.didYouMean(name, symbols);
     return new EvalException(getLocation(), "name '" + name + "' is not defined" + suggestion);
   }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
index 105768f..39a7673 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
@@ -47,6 +47,7 @@
   public abstract boolean incompatibleDisallowDictPlus();
   public abstract boolean incompatibleDisallowKeywordOnlyArgs();
   public abstract boolean incompatibleDisallowToplevelIfStatement();
+  public abstract boolean incompatibleDisallowUncalledSetConstructor();
   public abstract boolean incompatibleListPlusEqualsInplace();
   public abstract boolean incompatibleLoadArgumentIsLabel();
   public abstract boolean incompatibleNewActionsApi();
@@ -68,6 +69,7 @@
       .incompatibleDisallowDictPlus(false)
       .incompatibleDisallowKeywordOnlyArgs(true)
       .incompatibleDisallowToplevelIfStatement(true)
+      .incompatibleDisallowUncalledSetConstructor(false)
       .incompatibleListPlusEqualsInplace(true)
       .incompatibleLoadArgumentIsLabel(false)
       .incompatibleNewActionsApi(false)
@@ -89,6 +91,7 @@
     public abstract Builder incompatibleDisallowDictPlus(boolean value);
     public abstract Builder incompatibleDisallowKeywordOnlyArgs(boolean value);
     public abstract Builder incompatibleDisallowToplevelIfStatement(boolean value);
+    public abstract Builder incompatibleDisallowUncalledSetConstructor(boolean value);
     public abstract Builder incompatibleListPlusEqualsInplace(boolean value);
     public abstract Builder incompatibleLoadArgumentIsLabel(boolean value);
     public abstract Builder incompatibleNewActionsApi(boolean value);
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
index 451b0d5..cbe6094d 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
@@ -68,6 +68,12 @@
     block.variables.addAll(builtinVariables);
     block.readOnlyVariables.addAll(builtinVariables);
     semantics = env.getSemantics();
+
+    // If the flag is set to false, it should be allowed to have `set`
+    // in non-executable parts of the code.
+    if (!env.getSemantics().incompatibleDisallowUncalledSetConstructor()) {
+      block.variables.add("set");
+    }
   }
 
   @Override