diff --git a/vlib/builtin/string_interpolation.v b/vlib/builtin/string_interpolation.v
index 9d00ab94be..10064ac6ea 100644
--- a/vlib/builtin/string_interpolation.v
+++ b/vlib/builtin/string_interpolation.v
@@ -119,7 +119,7 @@ fn abs64(x i64) u64 {
 //=========================================
 
 // convert from data format to compact u64
-pub fn get_str_intp_u64_format(fmt_type StrIntpType, in_width int, in_precision int, in_tail_zeros bool, in_sign bool, in_pad_ch u8, in_base int, in_upper_case bool) u64 {
+pub fn get_str_intp_u64_format(fmt_type StrIntpType, in_width int, in_precision int, in_tail_zeros bool, in_sign bool, in_pad_ch byte, in_base int, in_upper_case bool) u64 {
 	width := if in_width != 0 { abs64(in_width) } else { u64(0) }
 	allign := if in_width > 0 { u64(1 << 5) } else { u64(0) } // two bit 0 .left 1 .rigth, for now we use only one
 	upper_case := if in_upper_case { u64(1 << 7) } else { u64(0) }
@@ -136,7 +136,7 @@ pub fn get_str_intp_u64_format(fmt_type StrIntpType, in_width int, in_precision
 }
 
 // convert from data format to compact u32
-pub fn get_str_intp_u32_format(fmt_type StrIntpType, in_width int, in_precision int, in_tail_zeros bool, in_sign bool, in_pad_ch u8, in_base int, in_upper_case bool) u32 {
+pub fn get_str_intp_u32_format(fmt_type StrIntpType, in_width int, in_precision int, in_tail_zeros bool, in_sign bool, in_pad_ch byte, in_base int, in_upper_case bool) u32 {
 	width := if in_width != 0 { abs64(in_width) } else { u32(0) }
 	allign := if in_width > 0 { u32(1 << 5) } else { u32(0) } // two bit 0 .left 1 .rigth, for now we use only one
 	upper_case := if in_upper_case { u32(1 << 7) } else { u32(0) }
diff --git a/vlib/v/gen/c/str_intp.v b/vlib/v/gen/c/str_intp.v
index 68e5830581..7ace443a12 100644
--- a/vlib/v/gen/c/str_intp.v
+++ b/vlib/v/gen/c/str_intp.v
@@ -110,7 +110,7 @@ fn (mut g Gen) str_format(node ast.StringInterLiteral, i int) (u64, string) {
 		pad_ch = 1
 	}
 	res := get_str_intp_u32_format(fmt_type, node.fwidths[i], node.precisions[i], remove_tail_zeros,
-		node.pluss[i], pad_ch, base, upper_case)
+		node.pluss[i], byte(pad_ch), base, upper_case)
 	//
 	return res, fmt_type.str()
 }