diff --git a/extmod/extmod.mk b/extmod/extmod.mk
index e312acba86db4..b000b058d7bd4 100644
--- a/extmod/extmod.mk
+++ b/extmod/extmod.mk
@@ -37,6 +37,8 @@ SRC_MOD += $(addprefix $(LITTLEFS_DIR)/,\
 	lfs2.c \
 	lfs2_util.c \
 	)
+
+$(BUILD)/$(LITTLEFS_DIR)/lfs2.o: CFLAGS += -Wno-missing-field-initializers
 endif
 
 ################################################################################
diff --git a/extmod/machine_i2c.c b/extmod/machine_i2c.c
index 9203f16f6d785..12c9abbcbaece 100644
--- a/extmod/machine_i2c.c
+++ b/extmod/machine_i2c.c
@@ -311,8 +311,8 @@ STATIC void mp_machine_soft_i2c_print(const mp_print_t *print, mp_obj_t self_in,
 STATIC void machine_i2c_obj_init_helper(machine_i2c_obj_t *self, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_scl, ARG_sda, ARG_freq, ARG_timeout };
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_scl, MP_ARG_REQUIRED | MP_ARG_OBJ },
-        { MP_QSTR_sda, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_scl, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_sda, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
         { MP_QSTR_freq, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 400000} },
         { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 255} },
     };
diff --git a/extmod/moductypes.c b/extmod/moductypes.c
index 811258424a3bf..c5fbf12e42b9d 100644
--- a/extmod/moductypes.c
+++ b/extmod/moductypes.c
@@ -506,6 +506,7 @@ STATIC mp_obj_t uctypes_struct_attr_op(mp_obj_t self_in, qstr attr, mp_obj_t set
                 return mp_obj_new_bytearray_by_ref(uctypes_struct_agg_size(sub, self->flags, &dummy), self->addr + offset);
             }
             // Fall thru to return uctypes struct object
+            MP_FALLTHROUGH
         }
         case PTR: {
             mp_obj_uctypes_struct_t *o = m_new_obj(mp_obj_uctypes_struct_t);
@@ -627,7 +628,7 @@ STATIC mp_obj_t uctypes_struct_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
                     return mp_obj_new_int((mp_int_t)(uintptr_t)p);
                 }
             }
-        /* fallthru */
+            MP_FALLTHROUGH
 
         default:
             return MP_OBJ_NULL;      // op not supported
diff --git a/extmod/re1.5/compilecode.c b/extmod/re1.5/compilecode.c
index 3f54b3993fd36..c4d12af87a32e 100644
--- a/extmod/re1.5/compilecode.c
+++ b/extmod/re1.5/compilecode.c
@@ -29,6 +29,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
                 prog->len++;
                 break;
             }
+            MP_FALLTHROUGH
         default:
             term = PC;
             EMIT(PC++, Char);
diff --git a/extmod/re1.5/recursiveloop.c b/extmod/re1.5/recursiveloop.c
index bb337decfbc95..f8cb92629200a 100644
--- a/extmod/re1.5/recursiveloop.c
+++ b/extmod/re1.5/recursiveloop.c
@@ -22,6 +22,7 @@ recursiveloop(char *pc, const char *sp, Subject *input, const char **subp, int n
 		case Char:
 			if(*sp != *pc++)
 				return 0;
+			MP_FALLTHROUGH
 		case Any:
 			sp++;
 			continue;
diff --git a/extmod/vfs_lfs.c b/extmod/vfs_lfs.c
index 9cf3eb11083cf..dd78269a460ab 100644
--- a/extmod/vfs_lfs.c
+++ b/extmod/vfs_lfs.c
@@ -35,7 +35,7 @@
 enum { LFS_MAKE_ARG_bdev, LFS_MAKE_ARG_readsize, LFS_MAKE_ARG_progsize, LFS_MAKE_ARG_lookahead, LFS_MAKE_ARG_mtime };
 
 static const mp_arg_t lfs_make_allowed_args[] = {
-    { MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ },
+    { MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
     { MP_QSTR_readsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 32} },
     { MP_QSTR_progsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 32} },
     { MP_QSTR_lookahead, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 32} },
diff --git a/mpy-cross/Makefile b/mpy-cross/Makefile
index f80ee761b7bcf..971f2f81aa593 100644
--- a/mpy-cross/Makefile
+++ b/mpy-cross/Makefile
@@ -18,7 +18,7 @@ INC += -I$(TOP)
 
 # compiler settings
 CWARN = -Wall -Werror
-CWARN += -Wpointer-arith -Wuninitialized
+CWARN += -Wextra -Wno-unused-parameter -Wpointer-arith
 CFLAGS = $(INC) $(CWARN) -std=gnu99 $(CFLAGS_MOD) $(COPT) $(CFLAGS_EXTRA)
 CFLAGS += -fdata-sections -ffunction-sections -fno-asynchronous-unwind-tables
 
diff --git a/ports/unix/Makefile b/ports/unix/Makefile
index ff5f355022bc5..7380e5e41259c 100644
--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -39,7 +39,7 @@ INC += -I$(BUILD)
 
 # compiler settings
 CWARN = -Wall -Werror
-CWARN += -Wpointer-arith -Wuninitialized -Wdouble-promotion -Wsign-compare -Wfloat-conversion
+CWARN += -Wextra -Wno-unused-parameter -Wpointer-arith -Wdouble-promotion -Wfloat-conversion
 CFLAGS += $(INC) $(CWARN) -std=gnu99 -DUNIX $(CFLAGS_MOD) $(COPT) -I$(VARIANT_DIR) $(CFLAGS_EXTRA)
 
 # Debugging/Optimization
diff --git a/py/emitinlinethumb.c b/py/emitinlinethumb.c
index 2853da26c5465..cffaa4bb89950 100644
--- a/py/emitinlinethumb.c
+++ b/py/emitinlinethumb.c
@@ -108,7 +108,7 @@ STATIC mp_uint_t emit_inline_thumb_count_params(emit_inline_asm_t *emit, mp_uint
             return 0;
         }
         const char *p = qstr_str(MP_PARSE_NODE_LEAF_ARG(pn_params[i]));
-        if (!(strlen(p) == 2 && p[0] == 'r' && p[1] == '0' + i)) {
+        if (!(strlen(p) == 2 && p[0] == 'r' && (mp_uint_t)p[1] == '0' + i)) {
             emit_inline_thumb_error_msg(emit, MP_ERROR_TEXT("parameters must be registers in sequence r0 to r3"));
             return 0;
         }
diff --git a/py/emitinlinextensa.c b/py/emitinlinextensa.c
index 6cc2e4d34b6a8..5dac2ae3907f1 100644
--- a/py/emitinlinextensa.c
+++ b/py/emitinlinextensa.c
@@ -92,7 +92,7 @@ STATIC mp_uint_t emit_inline_xtensa_count_params(emit_inline_asm_t *emit, mp_uin
             return 0;
         }
         const char *p = qstr_str(MP_PARSE_NODE_LEAF_ARG(pn_params[i]));
-        if (!(strlen(p) == 2 && p[0] == 'a' && p[1] == '2' + i)) {
+        if (!(strlen(p) == 2 && p[0] == 'a' && (mp_uint_t)p[1] == '2' + i)) {
             emit_inline_xtensa_error_msg(emit, MP_ERROR_TEXT("parameters must be registers in sequence a2 to a5"));
             return 0;
         }
diff --git a/py/gc.c b/py/gc.c
index 9c6336852a0cd..767f1b81c4dfa 100644
--- a/py/gc.c
+++ b/py/gc.c
@@ -298,7 +298,8 @@ STATIC void gc_sweep(void) {
                 #if MICROPY_PY_GC_COLLECT_RETVAL
                 MP_STATE_MEM(gc_collected)++;
                 #endif
-            // fall through to free the head
+                // fall through to free the head
+                MP_FALLTHROUGH
 
             case AT_TAIL:
                 if (free_tail) {
diff --git a/py/lexer.c b/py/lexer.c
index 7d2a251d41d75..07ea2b96ab578 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -346,7 +346,8 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw) {
                                 vstr_add_char(&lex->vstr, '\\');
                                 break;
                             }
-                        // Otherwise fall through.
+                            // Otherwise fall through.
+                            MP_FALLTHROUGH
                         case 'x': {
                             mp_uint_t num = 0;
                             if (!get_hex(lex, (c == 'x' ? 2 : c == 'u' ? 4 : 8), &num)) {
diff --git a/py/modmath.c b/py/modmath.c
index b7948f39e7c91..3ab3ff334c41b 100644
--- a/py/modmath.c
+++ b/py/modmath.c
@@ -206,8 +206,8 @@ MATH_FUN_1(lgamma, lgamma)
 STATIC mp_obj_t mp_math_isclose(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_a, ARG_b, ARG_rel_tol, ARG_abs_tol };
     static const mp_arg_t allowed_args[] = {
-        {MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ},
-        {MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ},
+        {MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL}},
+        {MP_QSTR_, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL}},
         {MP_QSTR_rel_tol, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL}},
         {MP_QSTR_abs_tol, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = MP_OBJ_NEW_SMALL_INT(0)}},
     };
diff --git a/py/mpconfig.h b/py/mpconfig.h
index cc83f3850d695..854188b66b585 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -1643,6 +1643,13 @@ typedef double mp_float_t;
 #endif
 #endif
 
+// Explicitly annotate switch case fall throughs
+#if defined(__GNUC__) && __GNUC__ >= 7
+#define MP_FALLTHROUGH __attribute__((fallthrough));
+#else
+#define MP_FALLTHROUGH
+#endif
+
 #ifndef MP_HTOBE16
 #if MP_ENDIANNESS_LITTLE
 #define MP_HTOBE16(x) ((uint16_t)((((x) & 0xff) << 8) | (((x) >> 8) & 0xff)))
diff --git a/py/objexcept.c b/py/objexcept.c
index 517427ed71365..885032c3e3eed 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -208,7 +208,7 @@ mp_obj_t mp_obj_exception_make_new(const mp_obj_type_t *type, size_t n_args, siz
         // reserved room (after the traceback data) for a tuple with 1 element.
         // Otherwise we are free to use the whole buffer after the traceback data.
         if (o_tuple == NULL && mp_emergency_exception_buf_size >=
-            EMG_BUF_TUPLE_OFFSET + EMG_BUF_TUPLE_SIZE(n_args)) {
+            (mp_int_t)(EMG_BUF_TUPLE_OFFSET + EMG_BUF_TUPLE_SIZE(n_args))) {
             o_tuple = (mp_obj_tuple_t *)
                 ((uint8_t *)MP_STATE_VM(mp_emergency_exception_buf) + EMG_BUF_TUPLE_OFFSET);
         }
@@ -383,7 +383,7 @@ mp_obj_t mp_obj_new_exception_msg(const mp_obj_type_t *exc_type, mp_rom_error_te
     // that buffer to store the string object, reserving room at the start for the
     // traceback and 1-tuple.
     if (o_str == NULL
-        && mp_emergency_exception_buf_size >= EMG_BUF_STR_OFFSET + sizeof(mp_obj_str_t)) {
+        && mp_emergency_exception_buf_size >= (mp_int_t)(EMG_BUF_STR_OFFSET + sizeof(mp_obj_str_t))) {
         o_str = (mp_obj_str_t *)((uint8_t *)MP_STATE_VM(mp_emergency_exception_buf)
             + EMG_BUF_STR_OFFSET);
     }
@@ -465,7 +465,7 @@ mp_obj_t mp_obj_new_exception_msg_vlist(const mp_obj_type_t *exc_type, mp_rom_er
     // that buffer to store the string object and its data (at least 16 bytes for
     // the string data), reserving room at the start for the traceback and 1-tuple.
     if ((o_str == NULL || o_str_buf == NULL)
-        && mp_emergency_exception_buf_size >= EMG_BUF_STR_OFFSET + sizeof(mp_obj_str_t) + 16) {
+        && mp_emergency_exception_buf_size >= (mp_int_t)(EMG_BUF_STR_OFFSET + sizeof(mp_obj_str_t) + 16)) {
         used_emg_buf = true;
         o_str = (mp_obj_str_t *)((uint8_t *)MP_STATE_VM(mp_emergency_exception_buf) + EMG_BUF_STR_OFFSET);
         o_str_buf = (byte *)((uint8_t *)MP_STATE_VM(mp_emergency_exception_buf) + EMG_BUF_STR_BUF_OFFSET);
@@ -573,7 +573,7 @@ void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, size_t line, qs
         self->traceback_data = m_new_maybe(size_t, TRACEBACK_ENTRY_LEN);
         if (self->traceback_data == NULL) {
             #if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
-            if (mp_emergency_exception_buf_size >= EMG_BUF_TRACEBACK_OFFSET + EMG_BUF_TRACEBACK_SIZE) {
+            if (mp_emergency_exception_buf_size >= (mp_int_t)(EMG_BUF_TRACEBACK_OFFSET + EMG_BUF_TRACEBACK_SIZE)) {
                 // There is room in the emergency buffer for traceback data
                 size_t *tb = (size_t *)((uint8_t *)MP_STATE_VM(mp_emergency_exception_buf)
                     + EMG_BUF_TRACEBACK_OFFSET);
diff --git a/py/objset.c b/py/objset.c
index f31a901a7008a..dac9b1138291e 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -445,6 +445,7 @@ STATIC mp_obj_t set_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
                 }
                 return MP_OBJ_NEW_SMALL_INT(hash);
             }
+            MP_FALLTHROUGH
         #endif
         default:
             return MP_OBJ_NULL;      // op not supported
diff --git a/py/scope.c b/py/scope.c
index 073c2a38c2c21..98e02fb53fe31 100644
--- a/py/scope.c
+++ b/py/scope.c
@@ -72,7 +72,7 @@ void scope_free(scope_t *scope) {
     m_del(scope_t, scope, 1);
 }
 
-id_info_t *scope_find_or_add_id(scope_t *scope, qstr qst, scope_kind_t kind) {
+id_info_t *scope_find_or_add_id(scope_t *scope, qstr qst, id_info_kind_t kind) {
     id_info_t *id_info = scope_find(scope, qst);
     if (id_info != NULL) {
         return id_info;
diff --git a/py/scope.h b/py/scope.h
index b52d98ea1c72d..edf164c4adace 100644
--- a/py/scope.h
+++ b/py/scope.h
@@ -29,14 +29,14 @@
 #include "py/parse.h"
 #include "py/emitglue.h"
 
-enum {
+typedef enum {
     ID_INFO_KIND_UNDECIDED,
     ID_INFO_KIND_GLOBAL_IMPLICIT,
     ID_INFO_KIND_GLOBAL_EXPLICIT,
     ID_INFO_KIND_LOCAL, // in a function f, written and only referenced by f
     ID_INFO_KIND_CELL,  // in a function f, read/written by children of f
     ID_INFO_KIND_FREE,  // in a function f, belongs to the parent of f
-};
+} id_info_kind_t;
 
 enum {
     ID_FLAG_IS_PARAM = 0x01,
@@ -92,7 +92,7 @@ typedef struct _scope_t {
 
 scope_t *scope_new(scope_kind_t kind, mp_parse_node_t pn, qstr source_file, mp_uint_t emit_options);
 void scope_free(scope_t *scope);
-id_info_t *scope_find_or_add_id(scope_t *scope, qstr qstr, scope_kind_t kind);
+id_info_t *scope_find_or_add_id(scope_t *scope, qstr qstr, id_info_kind_t kind);
 id_info_t *scope_find(scope_t *scope, qstr qstr);
 id_info_t *scope_find_global(scope_t *scope, qstr qstr);
 void scope_check_to_close_over(scope_t *scope, id_info_t *id);
diff --git a/py/vmentrytable.h b/py/vmentrytable.h
index 068214bf916cf..7912270872759 100644
--- a/py/vmentrytable.h
+++ b/py/vmentrytable.h
@@ -30,6 +30,10 @@
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Winitializer-overrides"
 #endif // __clang__
+#if __GNUC__ >= 5
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Woverride-init"
+#endif // __GNUC__ >= 5
 
 static const void *const entry_table[256] = {
     [0 ... 255] = &&entry_default,
@@ -119,3 +123,6 @@ static const void *const entry_table[256] = {
 #if __clang__
 #pragma clang diagnostic pop
 #endif // __clang__
+#if __GNUC__ >= 5
+#pragma GCC diagnostic pop
+#endif // __GNUC__ >= 5