diff --git a/include/fxos/lang.h b/include/fxos/lang.h
index c1e5964..6807b61 100644
--- a/include/fxos/lang.h
+++ b/include/fxos/lang.h
@@ -159,6 +159,14 @@ struct AsmInstruction
         IsDynamicJump = 0x40,
     };
 
+#define GENDEFS_INSN(NAME, STR) SH_##NAME,
+    enum {
+#include "gendefs/insn.h"
+        SH_MAX,
+    };
+#undef GENDEFS_INSN
+    static_assert(SH_MAX <= 0xff);
+
     AsmInstruction() = default;
 
     /* Construct with one or several arguments */
@@ -177,7 +185,7 @@ struct AsmInstruction
     u16 tags;
 
     /* Mnemonic **without the size indicator** */
-    char mnemonic[12];
+    char const *mnemonic() const;
     /* Arguments (up to 2) */
     AsmArgument args[2];
 
@@ -235,6 +243,10 @@ struct AsmInstruction
     /* Get the PC-relative target, assuming the instruction is at the provided
        address, for instructions with PC-relative offsets. */
     u32 getPCRelativeTarget(u32 pc) const;
+
+private:
+    /* Assembler instruction name (mov, add, etc), without size modifier. */
+    u8 m_opcode;
 };
 
 } /* namespace FxOS */
diff --git a/lib/disassembly.cpp b/lib/disassembly.cpp
index f6912ee..8c561c6 100644
--- a/lib/disassembly.cpp
+++ b/lib/disassembly.cpp
@@ -23,7 +23,7 @@ void register_instruction(AsmInstruction const &ins)
 
     if(insmap[encoding])
         FxOS_log(ERR, "encoding collision between a %s and a %s at %04x",
-            insmap[encoding]->mnemonic, ins.mnemonic, encoding);
+            insmap[encoding]->mnemonic(), ins.mnemonic(), encoding);
     else
         insmap[encoding] = ins;
 }
diff --git a/lib/lang.cpp b/lib/lang.cpp
index 33a6ebc..abaad9a 100644
--- a/lib/lang.cpp
+++ b/lib/lang.cpp
@@ -9,6 +9,7 @@
 #include <fxos/util/format.h>
 #include <string>
 #include <cstring>
+#include <cassert>
 
 namespace FxOS {
 
@@ -195,6 +196,12 @@ u32 AsmArgument::getPCRelativeTarget(u32 pc, int size) const
 //  Instruction management
 //---
 
+static char const *instructionMnemonics[] = {
+#define GENDEFS_INSN(NAME, STR) [AsmInstruction::SH_##NAME] = STR,
+#include "gendefs/insn.h"
+#undef GENDEFS_INSN
+};
+
 AsmInstruction::AsmInstruction(char const *mn):
     encoding {0}, opsize {0}, arg_count {0}
 {
@@ -214,9 +221,15 @@ AsmInstruction::AsmInstruction(char const *mn):
         len -= 2;
     }
 
-    len = std::min(len, 11);
-    strncpy(mnemonic, mn, len);
-    mnemonic[len] = 0;
+    int i;
+    for(i = 0; i < SH_MAX; i++) {
+        if(!strncmp(mn, instructionMnemonics[i], len)
+            && !instructionMnemonics[i][len]) {
+            m_opcode = i;
+            break;
+        }
+    }
+    assert(i < SH_MAX && "AsmInstruction with unknown opcode string");
 }
 
 AsmInstruction::AsmInstruction(char const *mn, AsmArgument arg):
@@ -235,6 +248,12 @@ AsmInstruction::AsmInstruction(
     arg_count = 2;
 }
 
+char const *AsmInstruction::mnemonic() const
+{
+    assert(m_opcode < SH_MAX);
+    return instructionMnemonics[m_opcode];
+}
+
 u32 AsmInstruction::getPCRelativeTarget(u32 pc) const
 {
     for(int i = 0; i < this->arg_count; i++) {
diff --git a/lib/view/assembly.cpp b/lib/view/assembly.cpp
index d8935c5..0d92a96 100644
--- a/lib/view/assembly.cpp
+++ b/lib/view/assembly.cpp
@@ -152,9 +152,10 @@ static void doOldInst(u32 pc, OldInstruction &i,
     static char const *suffixes[5] = {"", ".b", ".w", "", ".l"};
     char const *suffix = suffixes[(i.inst->opsize <= 4) ? i.inst->opsize : 0];
 
-    int spacing
-        = i.inst->arg_count ? 8 - strlen(i.inst->mnemonic) - strlen(suffix) : 0;
-    printf("   %s%s%*s", i.inst->mnemonic, suffix, spacing, "");
+    int spacing = i.inst->arg_count
+                      ? 8 - strlen(i.inst->mnemonic()) - strlen(suffix)
+                      : 0;
+    printf("   %s%s%*s", i.inst->mnemonic(), suffix, spacing, "");
 
     /* Arguments */
     for(size_t n = 0; n < i.inst->arg_count; n++) {
@@ -246,9 +247,9 @@ void viewAssemblyInstruction(Instruction const &ins, ViewAssemblyOptions *opts)
     char const *suffix = suffixes[(opcode.opsize <= 4) ? opcode.opsize : 0];
 
     int spacing
-        = opcode.arg_count ? 8 - strlen(opcode.mnemonic) - strlen(suffix) : 0;
+        = opcode.arg_count ? 8 - strlen(opcode.mnemonic()) - strlen(suffix) : 0;
     std::string str = "   ";
-    str += opcode.mnemonic;
+    str += opcode.mnemonic();
     str += suffix;
     str += std::string(spacing, ' ');