diff --git a/src/draw.c b/src/draw.c
index 8bce3c9..931f36c 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -61,12 +61,12 @@ static struct color hex_to_color(uint32_t hexValue, int dpc)
 static struct color string_to_color(const char *str)
 {
         char *end;
-        uint32_t val = strtoul(str+1, &end, 16);
-        if (*end != '\0' && *(end+1) != '\0') {
+        uint_fast32_t val = strtoul(str+1, &end, 16);
+        if (end[0] != '\0' && end[1] != '\0') {
                 LOG_W("Invalid color string: '%s'", str);
         }
 
-        switch (strlen(str+1)) {
+        switch (end - (str+1)) {
                 case 3:  return hex_to_color((val << 4) | 0xF, 1);
                 case 6:  return hex_to_color((val << 8) | 0xFF, 2);
                 case 4:  return hex_to_color(val, 1);