diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7459e8b08fc3d..b35587ff0857e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1686,7 +1686,8 @@ if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
           -DCMAKE_COLOR_DIAGNOSTICS:BOOLEAN=${CMAKE_COLOR_DIAGNOSTICS}
           -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
           -DSwiftCore_INSTALL_NESTED_SUBDIR=YES
-          -DSwiftCore_ENABLE_CONCURRENCY=${build_concurrency})
+          -DSwiftCore_ENABLE_CONCURRENCY=${build_concurrency}
+          -DCMAKE_OSX_SYSROOT:PATH=${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH})
       if(NOT ${CMAKE_CROSSCOMPILING})
         add_dependencies("${stdlib_target}-core" swift-frontend)
       endif()
@@ -1714,7 +1715,8 @@ if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
           -DCMAKE_COLOR_DIAGNOSTICS:BOOLEAN=${CMAKE_COLOR_DIAGNOSTICS}
           -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
           -DCMAKE_FIND_PACKAGE_PREFER_CONFIG=TRUE
-          -DSwiftOverlay_ENABLE_CXX_INTEROP=TRUE)
+          -DSwiftOverlay_ENABLE_CXX_INTEROP=TRUE
+          -DCMAKE_OSX_SYSROOT:PATH=${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH})
 
       ExternalProject_Add("${stdlib_target}-Supplemental"
         SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/Runtimes/Supplemental"
@@ -1739,7 +1741,8 @@ if(SWIFT_ENABLE_NEW_RUNTIME_BUILD)
           -DCMAKE_ASM_COMPILER_TARGET:STRING=${stdlib_target_triple}
           -DCMAKE_COLOR_DIAGNOSTICS:BOOLEAN=${CMAKE_COLOR_DIAGNOSTICS}
           -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
-          -DCMAKE_FIND_PACKAGE_PREFER_CONFIG=TRUE)
+          -DCMAKE_FIND_PACKAGE_PREFER_CONFIG=TRUE
+          -DCMAKE_OSX_SYSROOT:PATH=${SWIFT_SDK_${sdk}_ARCH_${arch}_PATH})
     endforeach()
   endforeach()
 endif()
diff --git a/Runtimes/Supplemental/CMakeLists.txt b/Runtimes/Supplemental/CMakeLists.txt
index 0b64b98c7c7e1..451b6ebdf0e88 100644
--- a/Runtimes/Supplemental/CMakeLists.txt
+++ b/Runtimes/Supplemental/CMakeLists.txt
@@ -42,6 +42,7 @@ set(COMMON_OPTIONS
   -DCMAKE_ASM_COMPILER_TARGET=${CMAKE_ASM_COMPILER_TARGET}
   -DCMAKE_Swift_COMPILER_TARGET=${CMAKE_Swift_COMPILER_TARGET}
   -DCMAKE_FIND_PACKAGE_PREFER_CONFIG=${CMAKE_FIND_PACKAGE_PREFER_CONFIG}
+  -DCMAKE_OSX_SYSROOT:PATH=${CMAKE_OSX_SYSROOT}
   ${SwiftCore_DIR_FLAG}
   ${MAKE_PROGRAM_FLAG})