diff --git a/lib/filters.h b/lib/filters.h
index 7b80352..6fac127 100644
--- a/lib/filters.h
+++ b/lib/filters.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <math.h>
 #include <string.h>
 #include <stdlib.h>
diff --git a/lib/fm_modulator.h b/lib/fm_modulator.h
index 2d57e59..7079a33 100644
--- a/lib/fm_modulator.h
+++ b/lib/fm_modulator.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "oscillator.h"
 
 typedef struct
diff --git a/lib/hilbert.h b/lib/hilbert.h
index 920fb6d..5e796ab 100644
--- a/lib/hilbert.h
+++ b/lib/hilbert.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include <stdlib.h>
 
 #define D_SIZE 256
diff --git a/lib/oscillator.h b/lib/oscillator.h
index c5db29a..69b794b 100644
--- a/lib/oscillator.h
+++ b/lib/oscillator.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "constants.h"
 #include "math.h"