diff --git a/q3DMASCClassifier.cpp b/q3DMASCClassifier.cpp
index 7a7464a..0fa1c6f 100644
--- a/q3DMASCClassifier.cpp
+++ b/q3DMASCClassifier.cpp
@@ -46,6 +46,10 @@
 #include <omp.h>
 #endif
 
+#if defined(__APPLE__)
+#include <unistd.h>
+#endif
+
 using namespace masc;
 
 Classifier::Classifier()