diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7962b29b..fb9c7a4e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,6 +38,7 @@ endif()
 
 set(BINDIR "${PROJECT_BINARY_DIR}/bin")
 set(LIBDIR "${PROJECT_BINARY_DIR}/lib")
+
 set(INCLUDE_INSTALL_DIR ${CMAKE_INSTALL_INCLUDEDIR})
 
 # First for the generic no-config case
@@ -57,6 +58,11 @@ if(CMAKE_GENERATOR STREQUAL Xcode)
     set(XCODE TRUE)
 endif()
 
+# older versions of cmake don't know things support isystem
+if (XCODE OR CMAKE_CXX_COMPILER_ID MATCHES "Intel")
+    set(CMAKE_INCLUDE_SYSTEM_FLAG_CXX "-isystem")
+endif ()
+
 set(CMAKE_INCLUDE_CURRENT_DIR 1)
 include_directories(${PROJECT_SOURCE_DIR}/src)
 include_directories(${PROJECT_BINARY_DIR})
@@ -402,13 +408,7 @@ CHECK_CXX_COMPILER_FLAG("-Wunused-variable" CXX_WUNUSED_VARIABLE)
 
 endif()
 
-if (NOT XCODE)
-    include_directories(SYSTEM ${Boost_INCLUDE_DIRS})
-else()
-    # cmake doesn't think Xcode supports isystem
-    set(EXTRA_CXX_FLAGS "${EXTRA_CXX_FLAGS} -isystem ${Boost_INCLUDE_DIRS}")
-endif()
-
+include_directories(SYSTEM ${Boost_INCLUDE_DIRS})
 
 if(CMAKE_SYSTEM_NAME MATCHES "Linux")
     set(LINUX TRUE)
diff --git a/tools/hsbench/CMakeLists.txt b/tools/hsbench/CMakeLists.txt
index 9b2cde4d..a8792cf7 100644
--- a/tools/hsbench/CMakeLists.txt
+++ b/tools/hsbench/CMakeLists.txt
@@ -4,12 +4,7 @@ if (NOT SQLITE3_FOUND)
     return()
 endif()
 
-if (NOT XCODE)
-    include_directories(SYSTEM ${SQLITE3_INCLUDE_DIRS})
-else()
-    # cmake doesn't think Xcode supports isystem
-    set(EXTRA_CXX_FLAGS "${EXTRA_CXX_FLAGS} -isystem ${SQLITE3_INCLUDE_DIRS}")
-endif()
+include_directories(SYSTEM ${SQLITE3_INCLUDE_DIRS})
 
 # BSD has the _np funcs in a _np header
 CHECK_INCLUDE_FILE_CXX(pthread_np.h HAVE_PTHREAD_NP_H)
diff --git a/unit/CMakeLists.txt b/unit/CMakeLists.txt
index 6f8a8bf4..e9d1821b 100644
--- a/unit/CMakeLists.txt
+++ b/unit/CMakeLists.txt
@@ -2,12 +2,7 @@ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${EXTRA_C_FLAGS}")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${EXTRA_CXX_FLAGS}")
 
 set(gtest_SOURCES gtest/gtest-all.cc gtest/gtest.h)
-if(NOT XCODE)
-    include_directories(SYSTEM ${CMAKE_CURRENT_SOURCE_DIR})
-else()
-    set(CMAKE_CXX_FLAGS "-isystem ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CXX_FLAGS}")
-endif()
-
+include_directories(SYSTEM ${CMAKE_CURRENT_SOURCE_DIR})
 include_directories(${PROJECT_SOURCE_DIR})
 
 # remove some warnings