diff --git a/src/float.c b/src/float.c
index 1361a36..7c02044 100644
--- a/src/float.c
+++ b/src/float.c
@@ -417,7 +417,7 @@
     void
 f_str2float(typval_T *argvars, typval_T *rettv)
 {
-    char_u *p = skipwhite(tv_get_string(&argvars[0]));
+    char_u *p = skipwhite(tv_get_string_strict(&argvars[0]));
     int     isneg = (*p == '-');
 
     if (*p == '+' || *p == '-')