diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -484,6 +484,9 @@
 
 add_subdirectory(utils/TableGen)
 
+# Export CLANG_TABLEGEN_EXE for use by flang docs.
+set(CLANG_TABLEGEN_EXE "${CLANG_TABLEGEN_EXE}" CACHE INTERNAL "")
+
 add_subdirectory(include)
 
 # All targets below may depend on all tablegen'd files.
diff --git a/flang/docs/CMakeLists.txt b/flang/docs/CMakeLists.txt
--- a/flang/docs/CMakeLists.txt
+++ b/flang/docs/CMakeLists.txt
@@ -126,7 +126,7 @@
         ARGS ${CMAKE_CURRENT_BINARY_DIR}/Source/FIR/CreateFIRLangRef.py)
 
       # CLANG_TABLEGEN_EXE variable needs to be set for clang_tablegen to run without error
-      set(CLANG_TABLEGEN_EXE clang-tblgen)
+      find_program(CLANG_TABLEGEN_EXE "clang-tblgen" ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
       gen_rst_file_from_td(FlangCommandLineReference.rst -gen-opt-docs FlangOptionsDocs.td docs-flang-html)
     endif()
     if (${SPHINX_OUTPUT_MAN})