diff --git a/llvm/test/LLVMBuild/enable-optional-component/Input/LLVMBuild.txt b/llvm/test/LLVMBuild/enable-optional-component/Input/LLVMBuild.txt
new file mode 100644
--- /dev/null
+++ b/llvm/test/LLVMBuild/enable-optional-component/Input/LLVMBuild.txt
@@ -0,0 +1,48 @@
+;===- ./LLVMBuild.txt ------------------------------------------*- Conf -*--===;
+;
+; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+; See https://llvm.org/LICENSE.txt for license information.
+; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[common]
+subdirectories = lib
+
+[component_0]
+type = LibraryGroup
+name = Engine
+parent = $ROOT
+
+[component_1]
+type = Library
+name = Interpreter
+parent = $ROOT
+
+[component_2]
+type = Group
+name = Miscellaneous
+parent = $ROOT
+
+[component_3]
+type = LibraryGroup
+name = Native
+parent = $ROOT
+
+[component_4]
+type = LibraryGroup
+name = NativeCodeGen
+parent = $ROOT
+
+[component_5]
+type = LibraryGroup
+name = all-targets
+parent = $ROOT
diff --git a/llvm/test/LLVMBuild/enable-optional-component/Input/lib/IR/Function.cpp b/llvm/test/LLVMBuild/enable-optional-component/Input/lib/IR/Function.cpp
new file mode 100644
diff --git a/llvm/test/LLVMBuild/enable-optional-component/Input/lib/LLVMBuild.txt b/llvm/test/LLVMBuild/enable-optional-component/Input/lib/LLVMBuild.txt
new file mode 100644
--- /dev/null
+++ b/llvm/test/LLVMBuild/enable-optional-component/Input/lib/LLVMBuild.txt
@@ -0,0 +1,30 @@
+;===- ./LLVMBuild.txt ------------------------------------------*- Conf -*--===;
+;
+; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+; See https://llvm.org/LICENSE.txt for license information.
+; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = OptionalLibrary
+name = Foo
+parent = $ROOT
+
+[component_1]
+type = OptionalLibrary
+name = FooBar
+parent = $ROOT
+
+[component_2]
+type = OptionalLibrary
+name = Z
+parent = $ROOT
diff --git a/llvm/test/LLVMBuild/enable-optional-component/enable-optional-component.test b/llvm/test/LLVMBuild/enable-optional-component/enable-optional-component.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/LLVMBuild/enable-optional-component/enable-optional-component.test
@@ -0,0 +1,24 @@
+RUN: %llvmbuild --source-root=%S/Input --write-llvmbuild=%T \
+RUN:     --enable-optional-components=Foo --write-library-table=%T/table.inc
+RUN: FileCheck %s < %T/lib/LLVMBuild.txt
+RUN: FileCheck --check-prefix=TABLE %s < %T/table.inc
+
+CHECK:      [component_0]
+CHECK-NEXT: type = OptionalLibrary
+CHECK-NEXT: name = Foo
+CHECK-NEXT: parent = $ROOT
+CHECK-NEXT: enabled_component = 1
+
+CHECK:      [component_1]
+CHECK-NEXT: type = OptionalLibrary
+CHECK-NEXT: name = FooBar
+CHECK-NEXT: parent = $ROOT
+
+CHECK:      [component_2]
+CHECK-NEXT: type = OptionalLibrary
+CHECK-NEXT: name = Z
+CHECK-NEXT: parent = $ROOT
+
+TABLE-NOT: FooBar
+TABLE: { "foo", "LLVMFoo"
+TABLE-NOT: FooBar
diff --git a/llvm/utils/llvm-build/llvmbuild/main.py b/llvm/utils/llvm-build/llvmbuild/main.py
--- a/llvm/utils/llvm-build/llvmbuild/main.py
+++ b/llvm/utils/llvm-build/llvmbuild/main.py
@@ -9,6 +9,15 @@
 
 ###
 
+def space_or_semicolon_list(x):
+    # We support both space separated and semi-colon separated lists.
+    if x == '':
+        return []
+    elif ' ' in x:
+        return x.split()
+    else:
+        return x.split(';')
+
 def cmake_quote_string(value):
     """
     cmake_quote_string(value) -> str
@@ -661,13 +670,7 @@
     if opts.enable_targets is None:
         enable_targets = available_targets.values()
     else:
-        # We support both space separated and semi-colon separated lists.
-        if opts.enable_targets == '':
-            enable_target_names = []
-        elif ' ' in opts.enable_targets:
-            enable_target_names = opts.enable_targets.split()
-        else:
-            enable_target_names = opts.enable_targets.split(';')
+        enable_target_names = space_or_semicolon_list(opts.enable_targets)
 
         enable_targets = []
         for name in enable_target_names:
@@ -791,6 +794,10 @@
     parser.add_option_group(group)
 
     (opts, args) = parser.parse_args()
+    opts.enable_optional_components = \
+        space_or_semicolon_list(opts.enable_optional_components)
+    opts.disable_optional_components = \
+        space_or_semicolon_list(opts.disable_optional_components)
 
     # Determine the LLVM source path, if not given.
     source_root = opts.source_root