diff --git a/openbsc/src/gsm_04_11.c b/openbsc/src/gsm_04_11.c
index 6290ce6..7a30653 100644
--- a/openbsc/src/gsm_04_11.c
+++ b/openbsc/src/gsm_04_11.c
@@ -262,7 +262,7 @@
 		if (cgbits & 2)
 			DEBUGP(DSMS, "Compressed SMS not supported yet\n");
 
-		switch (dcs & 3) {
+		switch ((dcs >> 2)&0x03) {
 		case 0:
 			alpha = DCS_7BIT_DEFAULT;
 			break;