diff --git a/py/compile.c b/py/compile.c
index ec6b463c05..5748256f24 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -3287,7 +3287,12 @@ STATIC void scope_compute_things(scope_t *scope) {
         #if MICROPY_EMIT_NATIVE
         if (id->kind == ID_INFO_KIND_GLOBAL_EXPLICIT) {
             // This function makes a reference to a global variable
-            scope->scope_flags |= MP_SCOPE_FLAG_REFGLOBALS;
+            if (scope->emit_options == MP_EMIT_OPT_VIPER
+                && mp_native_type_from_qstr(id->qst) >= MP_NATIVE_TYPE_INT) {
+                // A casting operator in viper mode, not a real global reference
+            } else {
+                scope->scope_flags |= MP_SCOPE_FLAG_REFGLOBALS;
+            }
         }
         #endif
         // params always count for 1 local, even if they are a cell
diff --git a/py/emitnative.c b/py/emitnative.c
index f791978dfb..4445aeaabd 100644
--- a/py/emitnative.c
+++ b/py/emitnative.c
@@ -66,7 +66,8 @@
 //                          locals (reversed, L0 at end)    |
 //
 // C stack layout for viper functions:
-//  0 = emit->stack_start:  nlr_buf_t [optional]            |
+//  0                       fun_obj, old_globals [optional]
+//  emit->stack_start:      nlr_buf_t [optional]            |
 //                          Python object stack             | emit->n_state
 //                          locals (reversed, L0 at end)    |
 //                          (L0-L2 may be in regs instead)
@@ -76,7 +77,7 @@
 
 // Whether the native/viper function needs to be wrapped in an exception handler
 #define NEED_GLOBAL_EXC_HANDLER(emit) ((emit)->scope->exc_stack_size > 0 \
-    || (!(emit)->do_viper_types && ((emit)->scope->scope_flags & MP_SCOPE_FLAG_REFGLOBALS)))
+    || ((emit)->scope->scope_flags & MP_SCOPE_FLAG_REFGLOBALS))
 
 // Whether registers can be used to store locals (only true if there are no
 // exception handlers, because otherwise an nlr_jump will restore registers to
@@ -312,8 +313,13 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
             }
         }
 
-        // The locals and stack start at the beginning of the C stack
-        emit->stack_start = 0;
+        // Work out where the locals and Python stack start within the C stack
+        if (NEED_GLOBAL_EXC_HANDLER(emit)) {
+            // Reserve 2 words for function object and old globals
+            emit->stack_start = 2;
+        } else {
+            emit->stack_start = 0;
+        }
 
         // Entry to function
         ASM_ENTRY(emit->as, emit->stack_start + emit->n_state - num_locals_in_regs);
@@ -325,6 +331,14 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
         asm_arm_mov_reg_i32(emit->as, ASM_ARM_REG_R7, (mp_uint_t)mp_fun_table);
         #endif
 
+        // Store function object (passed as first arg) to stack if needed
+        if (NEED_GLOBAL_EXC_HANDLER(emit)) {
+            #if N_X86
+            asm_x86_mov_arg_to_r32(emit->as, 0, REG_ARG_1);
+            #endif
+            ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_FUN_OBJ(emit), REG_ARG_1);
+        }
+
         // Put n_args in REG_ARG_1, n_kw in REG_ARG_2, args array in REG_LOCAL_3
         #if N_X86
         asm_x86_mov_arg_to_r32(emit->as, 1, REG_ARG_1);
@@ -931,15 +945,13 @@ STATIC void emit_native_global_exc_entry(emit_t *emit) {
         mp_uint_t start_label = *emit->label_slot + 2;
         mp_uint_t global_except_label = *emit->label_slot + 3;
 
-        if (!emit->do_viper_types) {
-            // Set new globals
-            ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_FUN_OBJ(emit));
-            ASM_LOAD_REG_REG_OFFSET(emit->as, REG_ARG_1, REG_ARG_1, offsetof(mp_obj_fun_bc_t, globals) / sizeof(uintptr_t));
-            emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
+        // Set new globals
+        ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_FUN_OBJ(emit));
+        ASM_LOAD_REG_REG_OFFSET(emit->as, REG_ARG_1, REG_ARG_1, offsetof(mp_obj_fun_bc_t, globals) / sizeof(uintptr_t));
+        emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
 
-            // Save old globals (or NULL if globals didn't change)
-            ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_OLD_GLOBALS(emit), REG_RET);
-        }
+        // Save old globals (or NULL if globals didn't change)
+        ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_OLD_GLOBALS(emit), REG_RET);
 
         if (emit->scope->exc_stack_size == 0) {
             // Optimisation: if globals didn't change don't push the nlr context
@@ -976,11 +988,9 @@ STATIC void emit_native_global_exc_entry(emit_t *emit) {
             ASM_JUMP_IF_REG_NONZERO(emit->as, REG_LOCAL_1, nlr_label, false);
         }
 
-        if (!emit->do_viper_types) {
-            // Restore old globals
-            ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_OLD_GLOBALS(emit));
-            emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
-        }
+        // Restore old globals
+        ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_OLD_GLOBALS(emit));
+        emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
 
         // Re-raise exception out to caller
         ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_EXC_VAL(emit));
@@ -996,19 +1006,17 @@ STATIC void emit_native_global_exc_exit(emit_t *emit) {
     emit_native_label_assign(emit, emit->exit_label);
 
     if (NEED_GLOBAL_EXC_HANDLER(emit)) {
-        if (!emit->do_viper_types) {
-            // Get old globals
-            ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_OLD_GLOBALS(emit));
+        // Get old globals
+        ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, LOCAL_IDX_OLD_GLOBALS(emit));
 
-            if (emit->scope->exc_stack_size == 0) {
-                // Optimisation: if globals didn't change then don't restore them and don't do nlr_pop
-                ASM_JUMP_IF_REG_ZERO(emit->as, REG_ARG_1, emit->exit_label + 1, false);
-            }
-
-            // Restore old globals
-            emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
+        if (emit->scope->exc_stack_size == 0) {
+            // Optimisation: if globals didn't change then don't restore them and don't do nlr_pop
+            ASM_JUMP_IF_REG_ZERO(emit->as, REG_ARG_1, emit->exit_label + 1, false);
         }
 
+        // Restore old globals
+        emit_call(emit, MP_F_NATIVE_SWAP_GLOBALS);
+
         // Pop the nlr context
         emit_call(emit, MP_F_NLR_POP);
         adjust_stack(emit, -(mp_int_t)(sizeof(nlr_buf_t) / sizeof(uintptr_t)));
diff --git a/tests/micropython/viper_globals.py b/tests/micropython/viper_globals.py
new file mode 100644
index 0000000000..9c68dc3da8
--- /dev/null
+++ b/tests/micropython/viper_globals.py
@@ -0,0 +1,19 @@
+# test that viper functions capture their globals context
+
+gl = {}
+
+exec("""
+@micropython.viper
+def f():
+    return x
+""", gl)
+
+# x is not yet in the globals, f should not see it
+try:
+    print(gl['f']())
+except NameError:
+    print('NameError')
+
+# x is in globals, f should now see it
+gl['x'] = 123
+print(gl['f']())
diff --git a/tests/micropython/viper_globals.py.exp b/tests/micropython/viper_globals.py.exp
new file mode 100644
index 0000000000..5731b89c1b
--- /dev/null
+++ b/tests/micropython/viper_globals.py.exp
@@ -0,0 +1,2 @@
+NameError
+123