diff --git a/CMakeLists.txt b/CMakeLists.txt
index dc884e9cc..e3bdaf673 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -159,27 +159,30 @@ find_package(Threads REQUIRED)
 # debug
 message(STATUS " CMAKE_THREAD_LIBS_INIT=${CMAKE_THREAD_LIBS_INIT}")
 message(STATUS " CMAKE_USE_PTHREADS_INIT=${CMAKE_USE_PTHREADS_INIT}")
-message(STATUS " ECCODES_THREADS=${ECCODES_THREADS}, HAVE_ECCODES_THREADS=${HAVE_ECCODES_THREADS}")
-
-if( NOT ${CMAKE_USE_PTHREADS_INIT} )
-    message( FATAL_ERROR "Only pthreads supported - thread library found is [${CMAKE_THREAD_LIBS_INIT}]" )
-endif()
+message(STATUS " HAVE_ECCODES_THREADS=${HAVE_ECCODES_THREADS}")
 
 set( GRIB_PTHREADS 0 )
 set( GRIB_OMP_THREADS 0 )
 set( GRIB_LINUX_PTHREADS 0 )
 #if( HAVE_ECCODES_THREADS AND CMAKE_THREAD_LIBS_INIT )
 if( HAVE_ECCODES_THREADS )
-    if( CMAKE_USE_PTHREADS_INIT )
-        set( GRIB_PTHREADS 1 )
-        if( ${CMAKE_SYSTEM_NAME} MATCHES "Linux" )
-            set( GRIB_LINUX_PTHREADS 1 )
-        endif()
+    if( NOT ${CMAKE_USE_PTHREADS_INIT} )
+        message( FATAL_ERROR "Pthreads is not supported on your system: thread library found=[${CMAKE_THREAD_LIBS_INIT}]" )
+    endif()
+    set( GRIB_PTHREADS 1 )
+    if( ${CMAKE_SYSTEM_NAME} MATCHES "Linux" )
+        set( GRIB_LINUX_PTHREADS 1 )
     endif()
 elseif(HAVE_ECCODES_OMP_THREADS)
     ecbuild_enable_omp()
     set( GRIB_OMP_THREADS 1 )
 endif()
+
+# Cannot have both options
+if( HAVE_ECCODES_THREADS AND HAVE_ECCODES_OMP_THREADS )
+    message( FATAL_ERROR "Cannot enable both POSIX threads and OMP! Please specify just one option" )
+endif()
+
 message(STATUS " GRIB_PTHREADS=${GRIB_PTHREADS}")
 message(STATUS " GRIB_OMP_THREADS=${GRIB_OMP_THREADS}")