diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -56,7 +56,6 @@
 check_include_file(termios.h HAVE_TERMIOS_H)
 check_include_file(unistd.h HAVE_UNISTD_H)
 check_include_file(valgrind/valgrind.h HAVE_VALGRIND_VALGRIND_H)
-check_include_file(zlib.h HAVE_ZLIB_H)
 check_include_file(fenv.h HAVE_FENV_H)
 check_symbol_exists(FE_ALL_EXCEPT "fenv.h" HAVE_DECL_FE_ALL_EXCEPT)
 check_symbol_exists(FE_INEXACT "fenv.h" HAVE_DECL_FE_INEXACT)
@@ -120,15 +119,30 @@
 if(NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
   set(HAVE_LIBZ 0)
   if(LLVM_ENABLE_ZLIB)
-    foreach(library z zlib_static zlib)
-      string(TOUPPER ${library} library_suffix)
-      check_library_exists(${library} compress2 "" HAVE_LIBZ_${library_suffix})
-      if(HAVE_LIBZ_${library_suffix})
-        set(HAVE_LIBZ 1)
-        set(ZLIB_LIBRARIES "${library}")
-        break()
+    if(ZLIB_ROOT OR ZLIB_LIBRARY OR ZLIB_INCLUDE_DIR)
+      include(FindZLIB)
+
+      if (ZLIB_FOUND)
+        include_directories(${ZLIB_INCLUDE_DIRS})
+        set(HAVE_ZLIB_H 1)
+        string(TOUPPER ${ZLIB_LIBRARIES} library_suffix)
+        check_library_exists(${ZLIB_LIBRARIES} compress2 "" HAVE_LIBZ_${library_suffix})
+        if(HAVE_LIBZ_${library_suffix})
+          set(HAVE_LIBZ 1)
+        endif()
       endif()
-    endforeach()
+    else()
+      check_include_file(zlib.h HAVE_ZLIB_H)
+      foreach(library z zlib_static zlib)
+        string(TOUPPER ${library} library_suffix)
+        check_library_exists(${library} compress2 "" HAVE_LIBZ_${library_suffix})
+        if(HAVE_LIBZ_${library_suffix})
+          set(HAVE_LIBZ 1)
+          set(ZLIB_LIBRARIES "${library}")
+          break()
+        endif()
+      endforeach()
+    endif()
   endif()
 
   # Don't look for these libraries on Windows.