diff --git a/folly/debugging/symbolizer/Elf.cpp b/folly/debugging/symbolizer/Elf.cpp
index 6a7f74f..6546fe0 100644
--- a/folly/debugging/symbolizer/Elf.cpp
+++ b/folly/debugging/symbolizer/Elf.cpp
@@ -49,6 +49,8 @@
 #define FOLLY_ELF_NATIVE_CLASS __WORDSIZE
 #endif // __ELF_NATIVE_CLASS
 
+#include <unistd.h>
+
 namespace folly {
 namespace symbolizer {