diff --git a/py/mpconfig.h b/py/mpconfig.h
index f9c02a6f0..8f60c997b 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -154,6 +154,12 @@ typedef double mp_float_t;
 #define MICROPY_PATH_MAX (512)
 #endif
 
+// Whether to use computed gotos in the VM, or a switch
+// Computed gotos are roughly 10% faster, and increase VM code size by a little
+#ifndef MICROPY_USE_COMPUTED_GOTO
+#define MICROPY_USE_COMPUTED_GOTO (0)
+#endif
+
 // Additional builtin function definitions - see builtintables.c:builtin_object_table for format.
 #ifndef MICROPY_EXTRA_BUILTINS
 #define MICROPY_EXTRA_BUILTINS
diff --git a/py/objstr.c b/py/objstr.c
index 08db2af66..fc1e1c569 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -662,7 +662,7 @@ mp_obj_t str_format(uint n_args, const mp_obj_t *args) {
             if (arg_i > 0) {
                 nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "cannot switch from automatic field numbering to manual field specification"));
             }
-            int index;
+            int index = 0;
             if (str_to_int(vstr_str(field_name), &index) != vstr_len(field_name) - 1) {
                 nlr_raise(mp_obj_new_exception_msg(&mp_type_KeyError, "attributes not supported yet"));
             }
diff --git a/py/vm.c b/py/vm.c
index f928ad694..6c117c7cb 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -167,7 +167,7 @@ mp_vm_return_kind_t mp_execute_byte_code_2(const byte *code_info, const byte **i
                                            volatile mp_obj_t inject_exc) {
     // careful: be sure to declare volatile any variables read in the exception handler (written is ok, I think)
 
-#ifdef MICROPY_USE_COMPUTED_GOTO
+#if MICROPY_USE_COMPUTED_GOTO
 
 #   define DISPATCH() do { \
       save_ip = ip; \
@@ -299,7 +299,7 @@ outer_dispatch_loop:
             // loop to execute byte code
             for (;;) {
 dispatch_loop:
-#ifdef MICROPY_USE_COMPUTED_GOTO
+#if MICROPY_USE_COMPUTED_GOTO
                 DISPATCH();
 #else
                 save_ip = ip;
@@ -1005,7 +1005,7 @@ yield:
                     nlr_pop();
                     fastn[0] = obj1;
                     return MP_VM_RETURN_EXCEPTION;
-#ifndef MICROPY_USE_COMPUTED_GOTO
+#if !MICROPY_USE_COMPUTED_GOTO
                 }
 #endif
             }
diff --git a/unix/Makefile b/unix/Makefile
index 64f5a6cf1..ac1baf3d0 100644
--- a/unix/Makefile
+++ b/unix/Makefile
@@ -11,7 +11,7 @@ QSTR_DEFS = qstrdefsport.h
 include ../py/py.mk
 
 # compiler settings
-CFLAGS = -I. -I$(PY_SRC) -Wall -Werror -ansi -std=gnu99 -DUNIX $(CFLAGS_MOD) $(COPT) -DMICROPY_USE_COMPUTED_GOTO
+CFLAGS = -I. -I$(PY_SRC) -Wall -Werror -ansi -std=gnu99 -DUNIX $(CFLAGS_MOD) $(COPT)
 
 UNAME_S := $(shell uname -s)
  ifeq ($(UNAME_S),Darwin)
diff --git a/unix/mpconfigport.h b/unix/mpconfigport.h
index fe35e5b09..75f119e91 100644
--- a/unix/mpconfigport.h
+++ b/unix/mpconfigport.h
@@ -14,6 +14,7 @@
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_DOUBLE)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_PATH_MAX            (PATH_MAX)
+#define MICROPY_USE_COMPUTED_GOTO   (1)
 #define MICROPY_MOD_SYS_STDFILES    (1)
 
 // type definitions for the specific machine