diff --git a/src/arch/alpha/isa/decoder.isa b/src/arch/alpha/isa/decoder.isa
index 7014d4c22..6df47ef7a 100644
--- a/src/arch/alpha/isa/decoder.isa
+++ b/src/arch/alpha/isa/decoder.isa
@@ -795,6 +795,12 @@ decode OPCODE default Unknown::unknown() {
             0x04: quiesceTime({{
                 R0 = AlphaPseudo::quiesceTime(xc->tcBase());
             }}, IsNonSpeculative, IsUnverifiable);
+            0x10: ivlb({{
+                warn_once("Obsolete M5 instruction ivlb encountered.\n");
+            }});
+            0x11: ivle({{
+                warn_once("Obsolete M5 instruction ivlb encountered.\n");
+            }});
             0x20: m5exit_old({{
                 AlphaPseudo::m5exit_old(xc->tcBase());
             }}, No_OpClass, IsNonSpeculative);
diff --git a/util/m5/m5op.S b/util/m5/m5op.S
index c47bd15b0..61e79d5d3 100644
--- a/util/m5/m5op.S
+++ b/util/m5/m5op.S
@@ -36,7 +36,9 @@
 #define quiescens_func 0x02
 #define quiescecycle_func 0x03
 #define quiescetime_func 0x04
-#define exit_old_func 0x20 // deprectated!
+#define ivlb 0x10 // obsolete
+#define ivle 0x11 // obsolete
+#define exit_old_func 0x20 // deprecated!
 #define exit_func 0x21
 #define initparam_func 0x30
 #define loadsymbol_func 0x31