diff --git a/cores/esp8266/core_esp8266_noniso.c b/cores/esp8266/core_esp8266_noniso.c
index e792048903..c499c1bcf3 100644
--- a/cores/esp8266/core_esp8266_noniso.c
+++ b/cores/esp8266/core_esp8266_noniso.c
@@ -29,62 +29,12 @@
 #include <math.h>
 #include "stdlib_noniso.h"
 
-void reverse(char* begin, char* end) {
-    char *is = begin;
-    char *ie = end - 1;
-    while(is < ie) {
-        char tmp = *ie;
-        *ie = *is;
-        *is = tmp;
-        ++is;
-        --ie;
-    }
-}
-
 char* ltoa(long value, char* result, int base) {
-    if(base < 2 || base > 16) {
-        *result = 0;
-        return result;
-    }
-
-    char* out = result;
-    long quotient = abs(value);
-
-    do {
-        const long tmp = quotient / base;
-        *out = "0123456789abcdef"[quotient - (tmp * base)];
-        ++out;
-        quotient = tmp;
-    } while(quotient);
-
-    // Apply negative sign
-    if(value < 0)
-        *out++ = '-';
-
-    reverse(result, out);
-    *out = 0;
-    return result;
+    return itoa((int)value, result, base);
 }
 
 char* ultoa(unsigned long value, char* result, int base) {
-    if(base < 2 || base > 16) {
-        *result = 0;
-        return result;
-    }
-
-    char* out = result;
-    unsigned long quotient = value;
-
-    do {
-        const unsigned long tmp = quotient / base;
-        *out = "0123456789abcdef"[quotient - (tmp * base)];
-        ++out;
-        quotient = tmp;
-    } while(quotient);
-
-    reverse(result, out);
-    *out = 0;
-    return result;
+    return utoa((unsigned int)value, result, base);
 }
 
 char * dtostrf(double number, signed char width, unsigned char prec, char *s) {
diff --git a/tests/host/common/noniso.c b/tests/host/common/noniso.c
index 21a26f02eb..869a4b7f8e 100644
--- a/tests/host/common/noniso.c
+++ b/tests/host/common/noniso.c
@@ -22,6 +22,17 @@
 #include "stdlib_noniso.h"
 
 
+void reverse(char* begin, char* end) {
+    char *is = begin;
+    char *ie = end - 1;
+    while(is < ie) {
+        char tmp = *ie;
+        *ie = *is;
+        *is = tmp;
+        ++is;
+        --ie;
+    }
+}
 
 char* utoa(unsigned value, char* result, int base) {
     if(base < 2 || base > 16) {
@@ -49,6 +60,9 @@ char* itoa(int value, char* result, int base) {
         *result = 0;
         return result;
     }
+    if (base != 10) {
+	return utoa((unsigned)value, result, base);
+   }
 
     char* out = result;
     int quotient = abs(value);
diff --git a/tests/host/core/test_string.cpp b/tests/host/core/test_string.cpp
index 39140b049b..ff13de8c79 100644
--- a/tests/host/core/test_string.cpp
+++ b/tests/host/core/test_string.cpp
@@ -115,6 +115,15 @@ TEST_CASE("String concantenation", "[core][String]")
     str = "clean";
     REQUIRE(str.concat(str) == true);
     REQUIRE(str == "cleanclean");
+    // non-decimal negative #s should be as if they were unsigned
+    str = String((int)-100, 16);
+    REQUIRE(str == "ffffff9c");
+    str = String((long)-101, 16);
+    REQUIRE(str == "ffffff9b");
+    str = String((int)-100, 10);
+    REQUIRE(str == "-100");
+    str = String((long)-100, 10);
+    REQUIRE(str == "-100");
 }
 
 TEST_CASE("String comparison", "[core][String]")