diff --git a/minmea.c b/minmea.c
index b40e07f..19957ed 100644
--- a/minmea.c
+++ b/minmea.c
@@ -221,8 +221,8 @@ bool minmea_scan(const char *sentence, const char *format, ...)
 
                 if (field[0] != '$')
                     goto parse_error;
-                for (int i=0; i<5; i++)
-                    if (!minmea_isfield(field[1+i]))
+                for (int f=0; f<5; f++)
+                    if (!minmea_isfield(field[f+i]))
                         goto parse_error;
 
                 char *buf = va_arg(ap, char *);
@@ -237,8 +237,8 @@ bool minmea_scan(const char *sentence, const char *format, ...)
 
                 if (field && minmea_isfield(*field)) {
                     // Always six digits.
-                    for (int i=0; i<6; i++)
-                        if (!isdigit((unsigned char) field[i]))
+                    for (int f=0; f<6; f++)
+                        if (!isdigit((unsigned char) field[f]))
                             goto parse_error;
 
                     d = strtol((char[]) {field[0], field[1], '\0'}, NULL, 10);
@@ -258,8 +258,8 @@ bool minmea_scan(const char *sentence, const char *format, ...)
 
                 if (field && minmea_isfield(*field)) {
                     // Minimum required: integer time.
-                    for (int i=0; i<6; i++)
-                        if (!isdigit((unsigned char) field[i]))
+                    for (int f=0; f<6; f++)
+                        if (!isdigit((unsigned char) field[f]))
                             goto parse_error;
 
                     h = strtol((char[]) {field[0], field[1], '\0'}, NULL, 10);