diff --git a/include/mes/lib-mini.h b/include/mes/lib-mini.h
index b3f24316..eb994f79 100644
--- a/include/mes/lib-mini.h
+++ b/include/mes/lib-mini.h
@@ -37,6 +37,15 @@
 #define STDERR 2
 #endif
 
+/* M2-Planet does not support pointer arithmetic.  Explicitly compensate
+   for that by multiplying with M2_PTR_SIZE when using (char)
+   pointers. */
+#if __M2__
+#define M2_PTR_SIZE 4
+#else
+#define M2_PTR_SIZE 1
+#endif
+
 extern char **environ;
 extern int __stdin;
 extern int __stdout;
diff --git a/include/mes/mes.h b/include/mes/mes.h
index 337f03aa..0323b2dc 100644
--- a/include/mes/mes.h
+++ b/include/mes/mes.h
@@ -53,6 +53,15 @@ struct scm
   };
 };
 
+/* M2-Planet does not support pointer arithmetic.  Explicitly compensate
+   for that by multiplying with M2_CELL_SIZE when using cell
+   pointers. */
+#if __M2__
+#define M2_CELL_SIZE 12
+#else
+#define M2_CELL_SIZE 1
+#endif
+
 /* mes */
 extern char *g_datadir;
 extern int g_debug;
diff --git a/lib/posix/getenv.c b/lib/posix/getenv.c
index 9386044b..e514f8c1 100644
--- a/lib/posix/getenv.c
+++ b/lib/posix/getenv.c
@@ -22,12 +22,6 @@
 #include <string.h>
 #include <stdlib.h>
 
-#if __M2__
-#define M2_PTR_SIZE 4
-#else
-#define M2_PTR_SIZE 1
-#endif
-
 char *
 getenv (char const *s)
 {
diff --git a/lib/posix/setenv.c b/lib/posix/setenv.c
index 1754e6e9..bdca5a7c 100644
--- a/lib/posix/setenv.c
+++ b/lib/posix/setenv.c
@@ -22,12 +22,6 @@
 #include <string.h>
 #include <stdlib.h>
 
-#if __M2__
-#define M2_PTR_SIZE 4
-#else
-#define M2_PTR_SIZE 1
-#endif
-
 int
 setenv (char const *s, char const *v, int overwrite_p)
 {
diff --git a/src/gc.c b/src/gc.c
index a55f24dc..8439536d 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -31,12 +31,6 @@
 
 int g_dump_filedes;
 
-#if __M2__
-#define M2_CELL_SIZE 12
-#else
-#define M2_CELL_SIZE 1U
-#endif
-
 char *
 cell_bytes (struct scm *x)
 {
diff --git a/src/symbol.c b/src/symbol.c
index 5d0aaaa2..55330fcd 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -23,12 +23,6 @@
 
 #include <string.h>
 
-#if __M2__
-#define M2_CELL_SIZE 12
-#else
-#define M2_CELL_SIZE 1
-#endif
-
 struct scm *
 init_symbol (struct scm *x, long type, char const *name)
 {
diff --git a/src/test/gc.c b/src/test/gc.c
index edafad8c..62960436 100644
--- a/src/test/gc.c
+++ b/src/test/gc.c
@@ -24,12 +24,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#if __M2__
-#define M2_CELL_SIZE 12
-#else
-#define M2_CELL_SIZE 1
-#endif
-
 int g_debug;
 
 void
diff --git a/src/vector.c b/src/vector.c
index e4a35ead..ad6b097b 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -21,12 +21,6 @@
 #include "mes/lib.h"
 #include "mes/mes.h"
 
-#if __M2__
-#define M2_CELL_SIZE 12
-#else
-#define M2_CELL_SIZE 1
-#endif
-
 struct scm *
 make_vector_ (long k, struct scm *e)
 {