diff --git a/include/osmocom/codec/codec.h b/include/osmocom/codec/codec.h
index 6f9ffea..81f5d4b 100644
--- a/include/osmocom/codec/codec.h
+++ b/include/osmocom/codec/codec.h
@@ -3,18 +3,18 @@
 
 #include <stdint.h>
 
-extern uint16_t gsm610_bitorder[];	/* FR */
-extern uint16_t gsm620_unvoiced_bitorder[]; /* HR unvoiced */
-extern uint16_t gsm620_voiced_bitorder[];   /* HR voiced */
-extern uint16_t gsm660_bitorder[];	/* EFR */
+extern const uint16_t gsm610_bitorder[];	/* FR */
+extern const uint16_t gsm620_unvoiced_bitorder[]; /* HR unvoiced */
+extern const uint16_t gsm620_voiced_bitorder[];   /* HR voiced */
+extern const uint16_t gsm660_bitorder[];	/* EFR */
 
-extern uint16_t gsm690_12_2_bitorder[];	/* AMR 12.2  kbits */
-extern uint16_t gsm690_10_2_bitorder[];	/* AMR 10.2  kbits */
-extern uint16_t gsm690_7_95_bitorder[];	/* AMR  7.95 kbits */
-extern uint16_t gsm690_7_4_bitorder[];	/* AMR  7.4  kbits */
-extern uint16_t gsm690_6_7_bitorder[];	/* AMR  6.7  kbits */
-extern uint16_t gsm690_5_9_bitorder[];	/* AMR  5.9  kbits */
-extern uint16_t gsm690_5_15_bitorder[];	/* AMR  5.15 kbits */
-extern uint16_t gsm690_4_75_bitorder[];	/* AMR  4.75 kbits */
+extern const uint16_t gsm690_12_2_bitorder[];	/* AMR 12.2  kbits */
+extern const uint16_t gsm690_10_2_bitorder[];	/* AMR 10.2  kbits */
+extern const uint16_t gsm690_7_95_bitorder[];	/* AMR  7.95 kbits */
+extern const uint16_t gsm690_7_4_bitorder[];	/* AMR  7.4  kbits */
+extern const uint16_t gsm690_6_7_bitorder[];	/* AMR  6.7  kbits */
+extern const uint16_t gsm690_5_9_bitorder[];	/* AMR  5.9  kbits */
+extern const uint16_t gsm690_5_15_bitorder[];	/* AMR  5.15 kbits */
+extern const uint16_t gsm690_4_75_bitorder[];	/* AMR  4.75 kbits */
 
 #endif /* _OSMOCOM_CODEC_H */