diff --git a/configure.ac b/configure.ac
index 9a5e1b7c2..86756534d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -112,7 +112,7 @@ AX_TYPE_SOCKLEN_T
 AX_CREATE_STDINT_H([eggint.h])
 
 # Checks for functions and their arguments.
-AC_CHECK_FUNCS([dprintf explicit_bzero memset_explicit explicit_memset getrandom inet_aton isascii memset_s snprintf strlcpy vsnprintf])
+AC_CHECK_FUNCS([dprintf explicit_bzero memset_explicit explicit_memset getrandom inet_aton memset_s snprintf strlcpy vsnprintf])
 AC_FUNC_SELECT_ARGTYPES
 EGG_FUNC_B64_NTOP
 AC_FUNC_MMAP