diff --git a/src/Makevars b/src/Makevars
index a3969dc..d685c69 100644
--- a/src/Makevars
+++ b/src/Makevars
@@ -1,4 +1,4 @@
 CXX_STD = CXX11
 
-PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
+PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS) -DARMA_DONT_USE_OPENMP
 PKG_LIBS     = $(SHLIB_OPENMP_CXXFLAGS) $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)
diff --git a/src/Makevars.win b/src/Makevars.win
index a3969dc..d685c69 100644
--- a/src/Makevars.win
+++ b/src/Makevars.win
@@ -1,4 +1,4 @@
 CXX_STD = CXX11
 
-PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
+PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS) -DARMA_DONT_USE_OPENMP
 PKG_LIBS     = $(SHLIB_OPENMP_CXXFLAGS) $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)