diff --git a/cmake/unix_compiler_options.cmake b/cmake/unix_compiler_options.cmake
index b53e9bf1a4..25ef82175c 100644
--- a/cmake/unix_compiler_options.cmake
+++ b/cmake/unix_compiler_options.cmake
@@ -14,7 +14,7 @@ if (${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
     set(PDAL_COMPILER_GCC 1)
 elseif (${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
     set(CXX_STANDARD "-std=c++11")
-    add_definitions("_GLIBCXX_USE_CXX11_ABI=1")
+    add_definitions("-D_GLIBCXX_USE_CXX11_ABI=1")
     set(PDAL_COMPILER_CLANG 1)
 else()
     message(FATAL_ERROR "Unsupported C++ compiler")