diff --git a/stdlib/CMakeLists.txt b/stdlib/CMakeLists.txt
index 4ad01abcad1b1..5c2400746cfa9 100644
--- a/stdlib/CMakeLists.txt
+++ b/stdlib/CMakeLists.txt
@@ -28,6 +28,14 @@ else()
   append("-fno-sanitize=all" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
+# Do not enforce checks for LLVM's ABI-breaking build settings.
+# The Swift runtime uses some header-only code from LLVM's ADT classes,
+# but we do not want to link libSupport into the runtime. These checks rely
+# on the presence of symbols in libSupport to identify how the code was
+# built and cause link failures for mismatches. Without linking that library,
+# we get link failures regardless, so instead, this just disables the checks.
+append("-DLLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING=1" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+
 set(SWIFT_STDLIB_LIBRARY_BUILD_TYPES)
 if(SWIFT_BUILD_DYNAMIC_STDLIB)
   list(APPEND SWIFT_STDLIB_LIBRARY_BUILD_TYPES SHARED)
diff --git a/utils/build-script-impl b/utils/build-script-impl
index 159c99bd412dd..617c6f32bd560 100755
--- a/utils/build-script-impl
+++ b/utils/build-script-impl
@@ -724,7 +724,6 @@ function set_build_options_for_host() {
     llvm_cmake_options+=(
         -DLLVM_TOOL_COMPILER_RT_BUILD:BOOL="$(false_true ${SKIP_BUILD_COMPILER_RT})"
         -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL="$(false_true ${SKIP_BUILD_COMPILER_RT})"
-        -DLLVM_DISABLE_ABI_BREAKING_CHECKS_ENFORCING:BOOL=TRUE
     )
 
     # If we are asked to not generate test targets for LLVM and or Swift,