1 files changed, 4 insertions, 0 deletions
diff --git a/psr.h b/psr.h
index 6a9d3ea..dfbb878 100644
--- a/psr.h
+++ b/psr.h
@@ -1,3 +1,6 @@
+#ifndef PSR_H
+#define PSR_H
+
 #include <stdint.h>
 
 enum execution_mode {
@@ -116,3 +119,4 @@ inline static void set_system_mode(void)
 // nop function, that just calls itself a given number of times)
 // doesn't have this magical property :(
 
+#endif // PSR_H