diff --git a/src/cmake/externalpackages.cmake b/src/cmake/externalpackages.cmake
index cccc6dc77..c07aa1227 100644
--- a/src/cmake/externalpackages.cmake
+++ b/src/cmake/externalpackages.cmake
@@ -192,6 +192,10 @@ if(NOT LLVM_DIRECTORY OR EXISTS ${LLVM_CONFIG})
        OUTPUT_STRIP_TRAILING_WHITESPACE)
 endif()
 
+if (LLVM_VERSION VERSION_GREATER 3.4.9 AND NOT OSL_BUILD_CPP11)
+    message (FATAL_ERROR "LLVM ${LLVM_VERSION} requires C++11. You must build with USE_CPP11=1.")
+endif ()
+
 find_library ( LLVM_LIBRARY
                NAMES LLVM-${LLVM_VERSION}
                PATHS ${LLVM_LIB_DIR})
@@ -235,7 +239,6 @@ if ((LLVM_LIBRARY OR LLVM_STATIC) AND LLVM_INCLUDES AND LLVM_DIRECTORY AND LLVM_
       message (STATUS "LLVM library  = ${LLVM_LIBRARY}")
   endif ()
 
-
   if (NOT LLVM_LIBRARY)
     message (FATAL_ERROR "LLVM library not found.")
   endif()
diff --git a/src/liboslexec/llvm_util.cpp b/src/liboslexec/llvm_util.cpp
index ce34b6511..949d6a06f 100644
--- a/src/liboslexec/llvm_util.cpp
+++ b/src/liboslexec/llvm_util.cpp
@@ -32,6 +32,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "OSL/oslconfig.h"
 #include "OSL/llvm_util.h"
 
+#if OSL_LLVM_VERSION >= 35 && ! OSL_BUILD_CPP11
+#error "LLVM >= 3.5 requires USE_CPP11=1"
+#endif
+
 #ifndef USE_MCJIT
   // MCJIT first appeared with LLVM 3.3
 # define USE_MCJIT (OSL_LLVM_VERSION>=33)