diff --git a/clang/cmake/caches/Fuchsia-stage2.cmake b/clang/cmake/caches/Fuchsia-stage2.cmake
--- a/clang/cmake/caches/Fuchsia-stage2.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2.cmake
@@ -211,14 +211,23 @@
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LLVM_BUILD_COMPILER_RT OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LLVM_USE_SANITIZER "Undefined" CACHE STRING "")
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+ubsan+noexcept_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+
     # Use .build-id link.
     list(APPEND RUNTIME_BUILD_ID_LINK "${target}-unknown-fuchsia")
   endforeach()
 
-  set(LLVM_RUNTIME_MULTILIBS "asan;noexcept;asan+noexcept" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIBS "asan;noexcept;asan+noexcept;ubsan;ubsan+noexcept" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_asan_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_asan+noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIB_ubsan_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIB_ubsan+noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
 endif()
 
 set(LLVM_BUILTIN_TARGETS "${BUILTIN_TARGETS}" CACHE STRING "")
diff --git a/clang/lib/Driver/ToolChains/Fuchsia.cpp b/clang/lib/Driver/ToolChains/Fuchsia.cpp
--- a/clang/lib/Driver/ToolChains/Fuchsia.cpp
+++ b/clang/lib/Driver/ToolChains/Fuchsia.cpp
@@ -202,11 +202,19 @@
   Multilibs.push_back(Multilib("noexcept", {}, {}, 1)
                           .flag("-fexceptions")
                           .flag("+fno-exceptions"));
+  // UBSan has lower priority than ASan so we pick the latter when both are set.
+  Multilibs.push_back(Multilib("ubsan", {}, {}, 2)
+                          .flag("+fsanitize=undefined"));
+  // Use the ubsan+noexcept variant with UBSan and -fno-exceptions.
+  Multilibs.push_back(Multilib("ubsan+noexcept", {}, {}, 3)
+                          .flag("+fsanitize=undefined")
+                          .flag("-fexceptions")
+                          .flag("+fno-exceptions"));
   // ASan has higher priority because we always want the instrumentated version.
-  Multilibs.push_back(Multilib("asan", {}, {}, 2)
+  Multilibs.push_back(Multilib("asan", {}, {}, 4)
                           .flag("+fsanitize=address"));
   // Use the asan+noexcept variant with ASan and -fno-exceptions.
-  Multilibs.push_back(Multilib("asan+noexcept", {}, {}, 3)
+  Multilibs.push_back(Multilib("asan+noexcept", {}, {}, 5)
                           .flag("+fsanitize=address")
                           .flag("-fexceptions")
                           .flag("+fno-exceptions"));
@@ -221,6 +229,7 @@
   addMultilibFlag(
       Args.hasFlag(options::OPT_fexceptions, options::OPT_fno_exceptions, true),
       "fexceptions", Flags);
+  addMultilibFlag(getSanitizerArgs().needsUbsanRt(), "fsanitize=undefined", Flags);
   addMultilibFlag(getSanitizerArgs().needsAsanRt(), "fsanitize=address", Flags);
   Multilibs.setFilePathsCallback(FilePaths);
 
diff --git a/clang/test/Driver/fuchsia.cpp b/clang/test/Driver/fuchsia.cpp
--- a/clang/test/Driver/fuchsia.cpp
+++ b/clang/test/Driver/fuchsia.cpp
@@ -71,23 +71,35 @@
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
 // RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86
-// RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=address \
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fno-exceptions \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
-// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-ASAN-X86
-// RUN: %clangxx %s -### --target=x86_64-fuchsia -fno-exceptions \
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-NOEXCEPT-X86
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=address \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
-// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-NOEXCEPT-X86
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-ASAN-X86
 // RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=address -fno-exceptions \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
 // RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-ASAN-NOEXCEPT-X86
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=undefined \
+// RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1\
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-UBSAN-X86
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=undefined -fno-exceptions \
+// RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1\
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-UBSAN-NOEXCEPT-X86
 // CHECK-MULTILIB-X86: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-MULTILIB-ASAN-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}asan+noexcept"
 // CHECK-MULTILIB-ASAN-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}asan"
+// CHECK-MULTILIB-UBSAN-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}ubsan+noexcept"
+// CHECK-MULTILIB-UBSAN-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}ubsan"
 // CHECK-MULTILIB-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}noexcept"
-// CHECK-MULTILIB-ASAN-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}asan+noexcept"
 // CHECK-MULTILIB-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++"