diff --git a/field.h b/field.h
index 7b5406e..e37eada 100644
--- a/field.h
+++ b/field.h
@@ -27,12 +27,3 @@ typedef enum {
 } Field_load_error;
 
 Field_load_error field_load_file(char const* filepath, Field* field);
-
-inline Glyph gbuffer_peek_relative(Gbuffer gbuffer, Usz height, Usz width,
-                                   Usz y, Usz x, Isz delta_y, Isz delta_x) {
-  Isz y0 = (Isz)y + delta_y;
-  Isz x0 = (Isz)x + delta_x;
-  if (y0 < 0 || x0 < 0 || (Usz)y0 >= height || (Usz)x0 >= width)
-    return '.';
-  return gbuffer[(Usz)y0 * width + (Usz)x0];
-}
diff --git a/gbuffer.h b/gbuffer.h
new file mode 100644
index 0000000..cfcf06f
--- /dev/null
+++ b/gbuffer.h
@@ -0,0 +1,11 @@
+#pragma once
+#include "base.h"
+
+inline Glyph gbuffer_peek_relative(Gbuffer gbuffer, Usz height, Usz width,
+                                   Usz y, Usz x, Isz delta_y, Isz delta_x) {
+  Isz y0 = (Isz)y + delta_y;
+  Isz x0 = (Isz)x + delta_x;
+  if (y0 < 0 || x0 < 0 || (Usz)y0 >= height || (Usz)x0 >= width)
+    return '.';
+  return gbuffer[(Usz)y0 * width + (Usz)x0];
+}
diff --git a/sim.c b/sim.c
index 07a2fa2..d66f894 100644
--- a/sim.c
+++ b/sim.c
@@ -1,5 +1,6 @@
 #include "field.h"
 #include "mark.h"
+#include "gbuffer.h"
 #include "sim.h"
 
 //////// Utilities