diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index d32413e4b4ce..d9c52387c4a1 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -3,6 +3,7 @@
  * Licensed under the GPL
  */
 
+#include <unistd.h>
 #include <stdio.h>
 #include <errno.h>
 #include <signal.h>