diff --git a/src/assembler/errors.c b/src/assembler/errors.c
index da75ecc..b74d519 100644
--- a/src/assembler/errors.c
+++ b/src/assembler/errors.c
@@ -43,10 +43,13 @@ static const char *error_descs[] = {
     [ED_SYM_DUPE_LABELS]  = "duplicate definitions for label",
     [ED_SYM_NO_LABEL]     = "undefined reference to label",
 
-    [ED_PARSE_OP_LONG]    = "opcode mnemonic is too long (2-4 characters)",
-    [ED_PARSE_OP_SHORT]   = "opcode mnemonic is too short (2-4 characters)",
-    [ED_PARSE_OP_CHARS]   = "invalid characters in opcode mnemonic",
-    [ED_PARSE_OP_UNKNOWN] = "unknown opcode mnemonic"
+    [ED_PS_OP_TOO_LONG]   = "opcode mnemonic is too long (2-4 characters)",
+    [ED_PS_OP_TOO_SHORT]  = "opcode mnemonic is too short (2-4 characters)",
+    [ED_PS_OP_INVALID]    = "invalid characters in opcode mnemonic",
+    [ED_PS_OP_UNKNOWN]    = "unknown opcode mnemonic",
+    [ED_PS_TOO_FEW_ARGS]  = "too few arguments for opcode",
+    [ED_PS_TOO_MANY_ARGS] = "too many arguments for opcode",
+    // [ED_PS_ARG1_TYPE]     = "invalid type for first argument",
 };
 
 /* Internal structs */
diff --git a/src/assembler/errors.h b/src/assembler/errors.h
index 100d745..4ed6da5 100644
--- a/src/assembler/errors.h
+++ b/src/assembler/errors.h
@@ -42,10 +42,12 @@ typedef enum {
     ED_SYM_DUPE_LABELS,
     ED_SYM_NO_LABEL,
 
-    ED_PARSE_OP_LONG,
-    ED_PARSE_OP_SHORT,
-    ED_PARSE_OP_CHARS,
-    ED_PARSE_OP_UNKNOWN
+    ED_PS_OP_TOO_LONG,
+    ED_PS_OP_TOO_SHORT,
+    ED_PS_OP_INVALID,
+    ED_PS_OP_UNKNOWN,
+    ED_PS_TOO_FEW_ARGS,
+    ED_PS_TOO_MANY_ARGS
 } ASMErrorDesc;
 
 /* Structs */
diff --git a/src/assembler/instructions.c b/src/assembler/instructions.c
index 36d849e..c7f2179 100644
--- a/src/assembler/instructions.c
+++ b/src/assembler/instructions.c
@@ -24,13 +24,66 @@
     page0     := $0 | $8 | $10 | $18 | $20 | $28 | $30 | $38
 */
 
+/* Helper macros for get_inst_parser() */
+
+#define JOIN_(a, b, c, d) ((uint32_t) ((a << 24) + (b << 16) + (c << 8) + d))
+
+#define DISPATCH_(s, z) (                                                     \
+    z == 2 ? JOIN_(s[0], s[1], 0x00, 0x00) :                                  \
+    z == 3 ? JOIN_(s[0], s[1], s[2], 0x00) :                                  \
+             JOIN_(s[0], s[1], s[2], s[3]))                                   \
+
+#define MAKE_CMP_(s) DISPATCH_(s, (sizeof(s) / sizeof(char) - 1))
+
+#define HANDLE(m) if (key == MAKE_CMP_(#m)) return parse_inst_##m;
+
+/* Instruction parser functions */
+
+#define INST_FUNC(mnemonic)                                                   \
+static ASMErrorDesc parse_inst_##mnemonic(                                    \
+    uint8_t **bytes, size_t *length, char **symbol, const char *arg, size_t size)
+
+INST_FUNC(nop)
+{
+    DEBUG("dispatched to -> NOP")
+    return ED_PS_TOO_FEW_ARGS;
+}
+
+INST_FUNC(inc)
+{
+    DEBUG("dispatched to -> INC")
+    return ED_PS_TOO_FEW_ARGS;
+}
+
+INST_FUNC(add)
+{
+    DEBUG("dispatched to -> ADD")
+    return ED_PS_TOO_FEW_ARGS;
+}
+
+INST_FUNC(adc)
+{
+    DEBUG("dispatched to -> ADC")
+    return ED_PS_TOO_FEW_ARGS;
+}
+
 /*
-    ...
+    Return the relevant ASMInstParser function for a given mnemonic.
+
+    NULL is returned if the mnemonic is not known.
 */
-ASMInstParser get_inst_parser(char mnemonic[MAX_MNEMONIC_SIZE + 1])
+ASMInstParser get_inst_parser(char mstr[MAX_MNEMONIC_SIZE])
 {
-    // TODO
-    DEBUG("get_inst_parser(): -->%s<--", mnemonic)
+    // Exploit the fact that we can store the entire mnemonic string as a
+    // single 32-bit value to do fast lookups:
+    uint32_t key = (mstr[0] << 24) + (mstr[1] << 16) + (mstr[2] << 8) + mstr[3];
+
+    DEBUG("get_inst_parser(): -->%.*s<-- 0x%08X", MAX_MNEMONIC_SIZE, mstr, key)
+
+    HANDLE(nop)
+    HANDLE(inc)
+    HANDLE(add)
+    HANDLE(adc)
 
     return NULL;
 }
diff --git a/src/assembler/instructions.h b/src/assembler/instructions.h
index 9d38d17..1aa0fc3 100644
--- a/src/assembler/instructions.h
+++ b/src/assembler/instructions.h
@@ -12,8 +12,9 @@
 
 /* Typedefs */
 
-typedef ASMErrorDesc (*ASMInstParser)(uint8_t**, size_t*, char**, const char*, size_t);
+typedef ASMErrorDesc (*ASMInstParser)(
+    uint8_t**, size_t*, char**, const char*, size_t);
 
 /* Functions */
 
-ASMInstParser get_inst_parser(char[MAX_MNEMONIC_SIZE + 1]);
+ASMInstParser get_inst_parser(char[MAX_MNEMONIC_SIZE]);
diff --git a/src/assembler/tokenizer.c b/src/assembler/tokenizer.c
index 9c70c41..a21188b 100644
--- a/src/assembler/tokenizer.c
+++ b/src/assembler/tokenizer.c
@@ -231,33 +231,32 @@ static ErrorInfo* parse_data(
 static ErrorInfo* parse_instruction(
     const ASMLine *line, ASMInstruction **inst_ptr, size_t offset)
 {
-    char mnemonic[MAX_MNEMONIC_SIZE + 1];
+    char mnemonic[MAX_MNEMONIC_SIZE] = {0};
     size_t i = 0;
     while (i < line->length) {
         char c = line->data[i];
         if (c == ' ')
             break;
         if (i >= MAX_MNEMONIC_SIZE)
-            return error_info_create(line, ET_PARSER, ED_PARSE_OP_LONG);
+            return error_info_create(line, ET_PARSER, ED_PS_OP_TOO_LONG);
         if ((c < 'a' || c > 'z') && (c < '0' || c > '9'))
-            return error_info_create(line, ET_PARSER, ED_PARSE_OP_CHARS);
+            return error_info_create(line, ET_PARSER, ED_PS_OP_INVALID);
         mnemonic[i++] = c;
     }
 
     if (i < MIN_MNEMONIC_SIZE)
-        return error_info_create(line, ET_PARSER, ED_PARSE_OP_SHORT);
+        return error_info_create(line, ET_PARSER, ED_PS_OP_TOO_SHORT);
 
     uint8_t *bytes;
     size_t arglen = line->length - i, length;
     char *argstart = arglen > 0 ? line->data + i : NULL, *symbol;
 
-    mnemonic[i] = '\0';
     ASMInstParser parser = get_inst_parser(mnemonic);
     if (!parser)
-        return error_info_create(line, ET_PARSER, ED_PARSE_OP_UNKNOWN);
+        return error_info_create(line, ET_PARSER, ED_PS_OP_UNKNOWN);
 
     ASMErrorDesc edesc = parser(&bytes, &length, &symbol, argstart, arglen);
-    if (edesc)
+    if (edesc != ED_NONE)
         return error_info_create(line, ET_PARSER, edesc);
 
     ASMInstruction *inst = malloc(sizeof(ASMInstruction));