diff --git a/vlib/builtin/float.v b/vlib/builtin/float.v
index f9faae9854..d990c1bb4a 100644
--- a/vlib/builtin/float.v
+++ b/vlib/builtin/float.v
@@ -2,7 +2,7 @@
 // Use of this source code is governed by an MIT license that can be found in the LICENSE file.
 module builtin
 
-import strconv.ftoa
+import strconv
 
 #include <float.h>
 // ----- f64 to string functions -----
@@ -11,9 +11,9 @@ import strconv.ftoa
 pub fn (x f64) str() string {
 	abs_x := f64_abs(x)
 	if abs_x >= 0.0001 && abs_x < 1.0e6 {
-		return ftoa.f64_to_str_l(x)
+		return strconv.f64_to_str_l(x)
 	} else {
-		return ftoa.ftoa_64(x)
+		return strconv.ftoa_64(x)
 	}
 }
 
@@ -31,13 +31,13 @@ pub fn (x f64) strsci(digit_num int) string {
 	} else if n_digit > 17 {
 		n_digit = 17
 	}
-	return ftoa.f64_to_str(x, n_digit)
+	return strconv.f64_to_str(x, n_digit)
 }
 
 // return a decimal notation of the input f64
 [inline]
 pub fn (x f64) strlong() string {
-	return ftoa.f64_to_str_l(x)
+	return strconv.f64_to_str_l(x)
 }
 
 // ----- f32 to string functions -----
@@ -46,9 +46,9 @@ pub fn (x f64) strlong() string {
 pub fn (x f32) str() string {
 	abs_x := f32_abs(x)
 	if abs_x >= 0.0001 && abs_x < 1.0e6 {
-		return ftoa.f32_to_str_l(x)
+		return strconv.f32_to_str_l(x)
 	} else {
-		return ftoa.ftoa_32(x)
+		return strconv.ftoa_32(x)
 	}
 }
 
@@ -61,13 +61,13 @@ pub fn (x f32) strsci(digit_num int) string {
 	} else if n_digit > 8 {
 		n_digit = 8
 	}
-	return ftoa.f32_to_str(x, n_digit)
+	return strconv.f32_to_str(x, n_digit)
 }
 
 // return a decimal notation of the input f32
 [inline]
 pub fn (x f32) strlong() string {
-	return ftoa.f32_to_str_l(x)
+	return strconv.f32_to_str_l(x)
 }
 
 // ----- C functions -----
diff --git a/vlib/strconv/atof_test.v b/vlib/strconv/atof_test.v
index 8253d4cc07..86b069c32d 100644
--- a/vlib/strconv/atof_test.v
+++ b/vlib/strconv/atof_test.v
@@ -4,7 +4,6 @@
 *
 **********************************************************************/
 import strconv
-import strconv.atofq
 
 fn test_atof() {
 	//
@@ -40,7 +39,7 @@ fn test_atof() {
 
 
 		// quick atof
-		mut s1 := (atofq.atof_quick(src_num_str[c]).str())
+		mut s1 := (atof_quick(src_num_str[c]).str())
 		mut s2 := (x.str())
 		delta := s1.f64() - s2.f64()
 		//println("$s1 $s2 $delta")
diff --git a/vlib/strconv/atofq/atofq.v b/vlib/strconv/atofq.v
similarity index 98%
rename from vlib/strconv/atofq/atofq.v
rename to vlib/strconv/atofq.v
index 438d126f5b..3517f7bdf5 100644
--- a/vlib/strconv/atofq/atofq.v
+++ b/vlib/strconv/atofq.v
@@ -16,15 +16,7 @@ Know limitation:
 
 */
 
-module atofq
-
-// same used in atof, here only for references
-const(
-	double_plus_zero        = u64(0x0000000000000000)
-	double_minus_zero       = u64(0x8000000000000000)
-	double_plus_infinity    = u64(0x7FF0000000000000)
-	double_minus_infinity   = u64(0xFFF0000000000000)
-)
+module strconv
 
 union Float64u {
 mut:
diff --git a/vlib/strconv/ftoa/f32_f64_to_string_test.v b/vlib/strconv/f32_f64_to_string_test.v
similarity index 100%
rename from vlib/strconv/ftoa/f32_f64_to_string_test.v
rename to vlib/strconv/f32_f64_to_string_test.v
diff --git a/vlib/strconv/ftoa/f32_str.v b/vlib/strconv/f32_str.v
similarity index 99%
rename from vlib/strconv/ftoa/f32_str.v
rename to vlib/strconv/f32_str.v
index 55ee20bf49..8544eca452 100644
--- a/vlib/strconv/ftoa/f32_str.v
+++ b/vlib/strconv/f32_str.v
@@ -17,7 +17,7 @@ inspired by the Go version here:
 https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 
 */
-module ftoa
+module strconv
 
 // dec32 is a floating decimal type representing m * 10^e.
 struct Dec32 {
diff --git a/vlib/strconv/ftoa/f64_str.v b/vlib/strconv/f64_str.v
similarity index 99%
rename from vlib/strconv/ftoa/f64_str.v
rename to vlib/strconv/f64_str.v
index 0b110ea03e..86f531b076 100644
--- a/vlib/strconv/ftoa/f64_str.v
+++ b/vlib/strconv/f64_str.v
@@ -17,7 +17,7 @@ inspired by the Go version here:
 https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 
 */
-module ftoa
+module strconv
 
 struct Uint128 {
 mut:
diff --git a/vlib/strconv/format.v b/vlib/strconv/format.v
index ef8211930b..e8e764f4a1 100644
--- a/vlib/strconv/format.v
+++ b/vlib/strconv/format.v
@@ -10,7 +10,7 @@ This file contains the printf/sprintf functions
 
 */
 module strconv
-import strconv.ftoa
+
 import strings
 
 enum Char_parse_state {
@@ -69,7 +69,7 @@ const(
 
 pub fn f64_to_str_lnd(f f64, dec_digit int) string {
 	// we add the rounding value
-	s := ftoa.f64_to_str(f + dec_round[dec_digit], 18)
+	s := f64_to_str(f + dec_round[dec_digit], 18)
 	// check for +inf -inf Nan
 	if s.len > 2 && (s[0] == `n` || s[1] == `i`) {
 		return s
@@ -77,7 +77,7 @@ pub fn f64_to_str_lnd(f f64, dec_digit int) string {
 
 	m_sgn_flag := false
 	mut sgn        := 1
-	mut b          := [26]byte 
+	mut b          := [26]byte
 	mut d_pos      := 1
 	mut i          := 0
 	mut i1         := 0
@@ -232,14 +232,14 @@ pub fn format_str(s string, p BF_param) string {
 	return res.str()
 }
 
-// max int64 9223372036854775807 
+// max int64 9223372036854775807
 pub fn format_dec(d u64, p BF_param) string {
 	mut s := ""
 	mut res := strings.new_builder(20)
 	mut sign_len_diff := 0
 	if p.pad_ch == `0` {
 		if p.positive {
-			if p.sign_flag { 
+			if p.sign_flag {
 				res.write_b(`+`)
 				sign_len_diff = -1
 			}
@@ -278,12 +278,12 @@ pub fn format_dec(d u64, p BF_param) string {
 pub fn format_fl(f f64, p BF_param) string {
 	mut s  := ""
 	mut fs := f64_to_str_lnd(if f >= 0.0 {f} else {-f}, p.len1)
-	
+
 	// error!!
 	if fs[0] == `[` {
 		return fs
 	}
-	
+
 	if p.rm_tail_zero {
 		fs = remove_tail_zeros(fs)
 	}
@@ -292,7 +292,7 @@ pub fn format_fl(f f64, p BF_param) string {
 	mut sign_len_diff := 0
 	if p.pad_ch == `0` {
 		if p.positive {
-			if p.sign_flag { 
+			if p.sign_flag {
 				res.write_b(`+`)
 				sign_len_diff = -1
 			}
@@ -332,7 +332,7 @@ pub fn format_fl(f f64, p BF_param) string {
 
 pub fn format_es(f f64, p BF_param) string {
 	mut s := ""
-	mut fs := ftoa.f64_to_str_pad(if f> 0 {f} else {-f},p.len1)
+	mut fs := f64_to_str_pad(if f> 0 {f} else {-f},p.len1)
 	if p.rm_tail_zero {
 		fs = remove_tail_zeros(fs)
 	}
@@ -341,7 +341,7 @@ pub fn format_es(f f64, p BF_param) string {
 	mut sign_len_diff := 0
 	if p.pad_ch == `0` {
 		if p.positive {
-			if p.sign_flag { 
+			if p.sign_flag {
 				res.write_b(`+`)
 				sign_len_diff = -1
 			}
@@ -441,7 +441,7 @@ pub fn v_sprintf(str string, pt ... voidptr) string{
 	mut pad_ch       := ` `              // pad char
 	mut th_separator := false            // thousands separator flag
 
-	// prefix chars for Length field 
+	// prefix chars for Length field
 	mut ch1 := `0`  // +1 char if present else `0`
 	mut ch2 := `0`  // +2 char if present else `0`
 
@@ -523,7 +523,7 @@ pub fn v_sprintf(str string, pt ... voidptr) string{
 				status = .check_float
 				i++
 				continue
-			} 
+			}
 			// manage "%.*s" precision field
 			else if ch == `.` && fc_ch1 == `*` && fc_ch2 == `s` {
 				len := unsafe {*(&int(pt[p_index]))}
@@ -748,7 +748,7 @@ pub fn v_sprintf(str string, pt ... voidptr) string{
 						*/
 						x := unsafe {*(&i64(pt[p_index]))}
 						s = x.hex()
-					} 
+					}
 					else {
 						x := unsafe {*(&int(pt[p_index]))}
 						s = x.hex()
diff --git a/vlib/strconv/ftoa/ftoa.v b/vlib/strconv/ftoa.v
similarity index 86%
rename from vlib/strconv/ftoa/ftoa.v
rename to vlib/strconv/ftoa.v
index 472e71a8c7..39708c931f 100644
--- a/vlib/strconv/ftoa/ftoa.v
+++ b/vlib/strconv/ftoa.v
@@ -9,15 +9,15 @@ that can be found in the LICENSE file.
 This file contains the f32/f64 ftoa functions
 
 These functions are based on the work of:
-Publication:PLDI 2018: Proceedings of the 39th ACM SIGPLAN 
-Conference on Programming Language Design and ImplementationJune 2018 
+Publication:PLDI 2018: Proceedings of the 39th ACM SIGPLAN
+Conference on Programming Language Design and ImplementationJune 2018
 Pages 270–282 https://doi.org/10.1145/3192366.3192369
 
-inspired by the Go version here: 
+inspired by the Go version here:
 https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 
 */
-module ftoa
+module strconv
 
 [inline]
 pub fn ftoa_64(f f64) string {
diff --git a/vlib/strconv/ftoa/tables.v b/vlib/strconv/tables.v
similarity index 99%
rename from vlib/strconv/ftoa/tables.v
rename to vlib/strconv/tables.v
index ce2d52d13b..519342e6f7 100644
--- a/vlib/strconv/ftoa/tables.v
+++ b/vlib/strconv/tables.v
@@ -1,4 +1,4 @@
-module ftoa
+module strconv
 
 const(
 pow5_num_bits_32     = 61
diff --git a/vlib/strconv/ftoa/utilities.v b/vlib/strconv/utilities.v
similarity index 99%
rename from vlib/strconv/ftoa/utilities.v
rename to vlib/strconv/utilities.v
index 34bb95b32e..f1b32ec7f0 100644
--- a/vlib/strconv/ftoa/utilities.v
+++ b/vlib/strconv/utilities.v
@@ -17,7 +17,7 @@ inspired by the Go version here:
 https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 
 */
-module ftoa
+module strconv
 
 import math.bits
 
diff --git a/vlib/v/builder/cc.v b/vlib/v/builder/cc.v
index 7907fa505d..c10ed6cd38 100644
--- a/vlib/v/builder/cc.v
+++ b/vlib/v/builder/cc.v
@@ -141,10 +141,8 @@ fn (mut v Builder) cc() {
 	// '-Werror',
 	// TODO : try and remove the below workaround options when the corresponding
 	// warnings are totally fixed/removed
-	mut a := [v.pref.cflags, '-std=gnu11', '-Wall', '-Wextra', '-Wno-unused-variable',
-		'-Wno-unused-parameter', '-Wno-unused-result', '-Wno-unused-function', '-Wno-missing-braces',
-		'-Wno-unused-label'
-	]
+	mut a := [v.pref.cflags, '-std=gnu11', '-Wall', '-Wextra', '-Wno-unused-variable', '-Wno-unused-parameter',
+		'-Wno-unused-result', '-Wno-unused-function', '-Wno-missing-braces', '-Wno-unused-label']
 	mut linker_flags := []string{}
 	// TCC on Linux by default, unless -cc was provided
 	// TODO if -cc = cc, TCC is still used, default compiler should be
@@ -357,9 +355,10 @@ fn (mut v Builder) cc() {
 	}
 	if v.pref.use_cache {
 		// vexe := pref.vexe_path()
-		cached_modules := ['builtin', 'os', 'math', 'strconv', 'strings']
+		cached_modules := ['builtin', 'os', 'math', 'strconv', 'strings', 'hash.wyhash', 'strconv.ftoa']
 		for cfile in cached_modules {
-			ofile := os.join_path(pref.default_module_path, 'cache', 'vlib', cfile + '.o')
+			ofile := os.join_path(pref.default_module_path, 'cache', 'vlib', cfile.replace('.', '/') +
+				'.o')
 			if !os.exists(ofile) {
 				println('${cfile}.o is missing. Building...')
 				println('$vexe build-module vlib/$cfile')
@@ -416,7 +415,7 @@ fn (mut v Builder) cc() {
 		println('=====================')
 		println('> C compiler cmd: $cmd')
 		if v.pref.show_cc {
-			println("> C compiler response file $response_file:")
+			println('> C compiler response file $response_file:')
 			println(response_file_content)
 		}
 		println('=====================')
@@ -478,7 +477,7 @@ fn (mut v Builder) cc() {
 		println('$ccompiler took $diff ms')
 		println('=========\n')
 	}
-    v.timing_message('C ${ccompiler:3}: ${diff}ms')
+	v.timing_message('C ${ccompiler:3}: ${diff}ms')
 	// Link it if we are cross compiling and need an executable
 	/*
 	if v.os == .linux && !linux_host && v.pref.build_mode != .build {
@@ -565,9 +564,7 @@ fn (mut b Builder) cc_linux_cross() {
 	}
 	linker_args := ['-L $sysroot/usr/lib/x86_64-linux-gnu/', '--sysroot=$sysroot -v -o $b.pref.out_name -m elf_x86_64',
 		'-dynamic-linker /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2', '$sysroot/crt1.o $sysroot/crti.o x.o',
-		'-lc', '-lcrypto', '-lssl', '-lpthread', '$sysroot/crtn.o',
-		cflags.c_options_only_object_files()
-	]
+		'-lc', '-lcrypto', '-lssl', '-lpthread', '$sysroot/crtn.o', cflags.c_options_only_object_files()]
 	// -ldl
 	linker_args_str := linker_args.join(' ')
 	cmd := '$sysroot/ld.lld ' + linker_args_str
diff --git a/vlib/v/builder/compile.v b/vlib/v/builder/compile.v
index 8fe4cc2f0a..7449a6566f 100644
--- a/vlib/v/builder/compile.v
+++ b/vlib/v/builder/compile.v
@@ -167,8 +167,10 @@ Did you forget to add vlib to the path? (Use @vlib for default vlib)')
 }
 
 pub fn (v &Builder) get_user_files() []string {
-	if v.pref.path in ['vlib/builtin', 'vlib/strconv', 'vlib/strings', 'vlib/hash'] {
-		// get_builtin_files() has already added the builtin files:
+	if v.pref.path in ['vlib/builtin', 'vlib/strconv', 'vlib/strings', 'vlib/hash', 'vlib/hash/wyhash'] {
+		// This means we are building a builtin module with `v build-module vlib/strings` etc
+		// get_builtin_files() has already added the files in this module,
+		// do nothing here to avoid duplicate definition errors.
 		v.log('Skipping user files.')
 		return []
 	}