diff --git a/CMakeLists.txt b/CMakeLists.txt
index fef0bf446c23c004a1f7ac190e084768eddd9ffd..8bc911b544c81606a44534b4fbf763b74c01a269 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -473,6 +473,7 @@ if(ENABLE_MPI)
    find_package(MPI)
    if(MPI_FOUND)
      message("-- Found MPI")
+     set(HAVE_MPI TRUE)
      set(HAVE_MPI TRUE PARENT_SCOPE) # export it for projects, too
      list(APPEND CONFIG_OPTIONS "MPI")
      list(APPEND EXTERNAL_INCLUDES ${MPI_INCLUDE_DIR})