diff --git a/src/write_coeff.cpp b/src/write_coeff.cpp
index 19f512fab1..685afc3c39 100644
--- a/src/write_coeff.cpp
+++ b/src/write_coeff.cpp
@@ -154,8 +154,8 @@ void WriteCoeff::command(int narg, char **arg)
           // parse type number and skip over it
           int type = std::stoi(str);
           char *p = str;
-          while ((*p != '\0') && (*p == ' ')) ++p;
-          while ((*p != '\0') && isdigit(*p)) ++p;
+          while (*p == ' ') ++p;
+          while (isdigit(*p)) ++p;
 
           fprintf(two, "%s %d %s %s", coeff, type, section, p);
           utils::sfgets(FLERR, str, BUF_SIZE, one, file, error);