diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 3c66eecbf0..edd45d411d 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -308,7 +308,8 @@ const (
 	ABaseMIPS64
 	ABaseS390X
 
-	AMask = 1<<12 - 1 // AND with this to use the opcode as an array index.
+	AllowedOpCodes = 1 << 12            // The number of opcodes available for any given architecture.
+	AMask          = AllowedOpCodes - 1 // AND with this to use the opcode as an array index.
 )
 
 // An LSym is the sort of symbol that is written to an object file.
diff --git a/src/cmd/internal/obj/util.go b/src/cmd/internal/obj/util.go
index a80af26c07..1572071ed3 100644
--- a/src/cmd/internal/obj/util.go
+++ b/src/cmd/internal/obj/util.go
@@ -462,6 +462,9 @@ var aSpace []opSet
 // RegisterOpcode binds a list of instruction names
 // to a given instruction number range.
 func RegisterOpcode(lo As, Anames []string) {
+	if len(Anames) > AllowedOpCodes {
+		panic(fmt.Sprintf("too many instructions, have %d max %d", len(Anames), AllowedOpCodes))
+	}
 	aSpace = append(aSpace, opSet{lo, Anames})
 }