diff --git a/src/encoding.cpp b/src/encoding.cpp
index c24d187..67defec 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -447,7 +447,7 @@
 
 	bitvec_write_field(dest, &wp, 0x0, 4);  // Skip Indicator
 	bitvec_write_field(dest, &wp, 0x6, 4);  // Protocol Discriminator
-	bitvec_write_field(dest, &wp, 0x3F, 8); // Immediate Assignment Message Type
+	bitvec_write_field(dest, &wp, GSM48_MT_RR_IMM_ASS, 8); // Immediate Assignment Message Type
 
 	// 10.5.2.25b Dedicated mode or TBF
 	bitvec_write_field(dest, &wp, 0x0, 1);      // spare