diff --git a/configure.ac b/configure.ac
index f930c90..eb715e8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8,7 +8,7 @@ AC_CONFIG_SRCDIR([config.h.in])
 AC_CONFIG_HEADERS([config.h])
 
 # Checks for programs.
-AC_PROG_CC
+AC_PROG_CC_C99
 AC_PROG_LEX
 AC_PROG_YACC
 
@@ -24,16 +24,20 @@ AC_CHECK_HEADERS([inttypes.h libintl.h limits.h malloc.h stddef.h stdint.h stdli
 AC_C_INLINE
 AC_TYPE_INT16_T
 AC_TYPE_INT32_T
+AC_TYPE_INT64_T
 AC_TYPE_INT8_T
+AC_TYPE_PID_T
 AC_TYPE_SIZE_T
 AC_TYPE_UINT16_T
 AC_TYPE_UINT32_T
+AC_TYPE_UINT64_T
 AC_TYPE_UINT8_T
 
 # Checks for library functions.
+AC_FUNC_FORK
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
-AC_CHECK_FUNCS([memset pledge realpath strdup strndup])
+AC_CHECK_FUNCS([localtime_r pledge memset realpath strcasecmp strdup strndup strrchr])
 
 AC_CONFIG_FILES([Makefile
                  data/Makefile