diff --git a/compiler/capnpc-c.c b/compiler/capnpc-c.c
index 3e2ede2..30849cc 100644
--- a/compiler/capnpc-c.c
+++ b/compiler/capnpc-c.c
@@ -418,6 +418,27 @@ static void decode_value(struct value* v, Type_ptr type, Value_ptr value, const
 
 static void define_const(struct node *n) {
 	struct value v;
+	const char *p;
+	char *name_snake, *s;
+
+	/* convert camelCase name to SCREAMING_SNAKE_CASE */
+	name_snake = malloc(strlen(n->name.str) * 2);
+	s = name_snake;
+	p = n->name.str;
+	while (*p) {
+		const char *next_p = p + 1;
+
+		*s = toupper(*p);
+		s++;
+
+		if (*next_p &&  islower(*p) && isupper(*next_p)) {
+			*s = '_';
+			s++;
+		}
+		p++;
+	}
+	*s = 0;
+
 	decode_value(&v, n->n._const.type, n->n._const.value, n->name.str);
 
 	switch (v.v.which) {
@@ -425,45 +446,51 @@ static void define_const(struct node *n) {
 	case Value_int8:
 	case Value_int16:
 	case Value_int32:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = %d;\n", v.tname, n->name.str, (int) v.intval);
+		str_addf(&HDR, "#define %s (%d)\n", name_snake, (int) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = %s;\n", v.tname, n->name.str, name_snake);
 		break;
 
 	case Value_uint8:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = %u;\n", v.tname, n->name.str, (uint8_t) v.intval);
+		str_addf(&HDR, "#define %s (%u)\n", name_snake, (uint8_t) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = %s;\n", v.tname, n->name.str, name_snake);
 		break;
 
 	case Value_uint16:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = %u;\n", v.tname, n->name.str, (uint16_t) v.intval);
+		str_addf(&HDR, "#define %s (%u)\n", name_snake, (uint16_t) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = %s;\n", v.tname, n->name.str, name_snake);
 		break;
 
 	case Value_uint32:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = %uu;\n", v.tname, n->name.str, (uint32_t) v.intval);
+		str_addf(&HDR, "#define %s (%uu)\n", name_snake, (uint32_t) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = %s;\n", v.tname, n->name.str, name_snake);
 		break;
 
 	case Value__enum:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = (%s) %uu;\n", v.tname, n->name.str, v.tname, (uint32_t) v.intval);
+		str_addf(&HDR, "#define %s (%uu)\n", name_snake, (uint32_t) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = (%s) %s;\n", v.tname, n->name.str, v.tname, name_snake);
 		break;
 
 	case Value_int64:
 	case Value_uint64:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
-		str_addf(&SRC, "%s %s = ((uint64_t) %#xu << 32) | %#xu;\n", v.tname, n->name.str,
+		str_addf(&HDR, "#define %s (((uint64_t) %#xu << 32) | %#xu)\n", name_snake,
 				(uint32_t) (v.intval >> 32), (uint32_t) v.intval);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
+		str_addf(&SRC, "const %s %s = %s;\n", v.tname, n->name.str, name_snake);
 		break;
 
 	case Value_float32:
-		str_addf(&HDR, "extern union capn_conv_f32 %s;\n", n->name.str);
-		str_addf(&SRC, "union capn_conv_f32 %s = {%#xu};\n", n->name.str, (uint32_t) v.intval);
+		str_addf(&HDR, "extern const union capn_conv_f32 %s;\n", n->name.str);
+		str_addf(&SRC, "const union capn_conv_f32 %s = {%#xu};\n", n->name.str, (uint32_t) v.intval);
 		break;
 
 	case Value_float64:
-		str_addf(&HDR, "extern union capn_conv_f64 %s;\n", n->name.str);
-		str_addf(&SRC, "union capn_conv_f64 %s = {((uint64_t) %#xu << 32) | %#xu};\n",
+		str_addf(&HDR, "extern const union capn_conv_f64 %s;\n", n->name.str);
+		str_addf(&SRC, "const union capn_conv_f64 %s = {((uint64_t) %#xu << 32) | %#xu};\n",
 				n->name.str, (uint32_t) (v.intval >> 32), (uint32_t) v.intval);
 		break;
 
@@ -472,9 +499,9 @@ static void define_const(struct node *n) {
 	case Value__struct:
 	case Value_anyPointer:
 	case Value__list:
-		str_addf(&HDR, "extern %s %s;\n", v.tname, n->name.str);
+		str_addf(&HDR, "extern const %s %s;\n", v.tname, n->name.str);
 		if (!v.ptrval.type) {
-			str_addf(&SRC, "%s %s;\n", v.tname, n->name.str);
+			str_addf(&SRC, "const %s %s;\n", v.tname, n->name.str);
 		}
 		break;
 
@@ -484,6 +511,7 @@ static void define_const(struct node *n) {
 	}
 
 	str_release(&v.tname_buf);
+	free(name_snake);
 }
 
 static void decode_field(struct field *fields, Field_list l, int i) {