diff --git a/configure.ac b/configure.ac
index 5336a21d3..ac6bd4b6a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -382,62 +382,63 @@ AC_DEFUN([RB_CHK_SYSHEADER],
 
 AC_HEADER_STDBOOL
 dnl AC_HEADER_STDC
-RB_CHK_SYSHEADER([assert.h],       [ASSERT_H])
-RB_CHK_SYSHEADER([stdarg.h],       [STDARG_H])
-RB_CHK_SYSHEADER([sys/time.h],     [SYS_TIME_H])
+RB_CHK_SYSHEADER([assert.h], [ASSERT_H])
+RB_CHK_SYSHEADER([stdarg.h], [STDARG_H])
+RB_CHK_SYSHEADER([sys/time.h], [SYS_TIME_H])
 RB_CHK_SYSHEADER([sys/resource.h], [SYS_RESOURCE_H])
-RB_CHK_SYSHEADER([cstddef],        [CSTDDEF])
-RB_CHK_SYSHEADER([cstdint],        [CSTDINT])
-RB_CHK_SYSHEADER([limits],         [LIMITS])
-RB_CHK_SYSHEADER([type_traits],    [TYPE_TRAITS])
-RB_CHK_SYSHEADER([typeindex],      [TYPEINDEX])
-RB_CHK_SYSHEADER([variant],        [VARIANT])
-RB_CHK_SYSHEADER([utility],        [UTILITY])
-RB_CHK_SYSHEADER([functional],     [FUNCTIONAL])
-RB_CHK_SYSHEADER([algorithm],      [ALGORITHM])
-RB_CHK_SYSHEADER([numeric],        [NUMERIC])
-RB_CHK_SYSHEADER([cmath],          [CMATH])
-RB_CHK_SYSHEADER([memory],         [MEMORY])
-RB_CHK_SYSHEADER([exception],      [EXCEPTION])
-RB_CHK_SYSHEADER([cerrno],         [CERRNO])
-RB_CHK_SYSHEADER([system_error],   [SYSTEM_ERROR])
-RB_CHK_SYSHEADER([map],            [MAP])
-RB_CHK_SYSHEADER([set],            [SET])
-RB_CHK_SYSHEADER([list],           [LIST])
-RB_CHK_SYSHEADER([stack],          [STACK])
-RB_CHK_SYSHEADER([queue],          [QUEUE])
-RB_CHK_SYSHEADER([deque],          [DEQUE])
-RB_CHK_SYSHEADER([array],          [ARRAY])
-RB_CHK_SYSHEADER([vector],         [VECTOR])
-RB_CHK_SYSHEADER([forward_list],   [FORWARD_LIST])
-RB_CHK_SYSHEADER([unordered_map],  [UNORDERED_MAP])
-RB_CHK_SYSHEADER([string],         [STRING])
-RB_CHK_SYSHEADER([cstring],        [CSTRING])
-RB_CHK_SYSHEADER([locale],         [LOCALE])
-RB_CHK_SYSHEADER([codecvt],        [CODECVT])
-RB_CHK_SYSHEADER([sstream],        [SSTREAM])
-RB_CHK_SYSHEADER([fstream],        [FSTREAM])
-RB_CHK_SYSHEADER([iostream],       [IOSTREAM])
-RB_CHK_SYSHEADER([iomanip],        [IOMANIP])
-RB_CHK_SYSHEADER([cstdio],         [CSTDIO])
-RB_CHK_SYSHEADER([chrono],         [CHRONO])
-RB_CHK_SYSHEADER([ctime],          [CTIME])
-RB_CHK_SYSHEADER([atomic],         [ATOMIC])
-RB_CHK_SYSHEADER([thread],         [THREAD])
-RB_CHK_SYSHEADER([mutex],          [MUTEX])
-RB_CHK_SYSHEADER([shared_mutex],   [SHARED_MUTEX])
+RB_CHK_SYSHEADER([cstddef], [CSTDDEF])
+RB_CHK_SYSHEADER([cstdint], [CSTDINT])
+RB_CHK_SYSHEADER([limits], [LIMITS])
+RB_CHK_SYSHEADER([type_traits], [TYPE_TRAITS])
+RB_CHK_SYSHEADER([typeindex], [TYPEINDEX])
+RB_CHK_SYSHEADER([variant], [VARIANT])
+RB_CHK_SYSHEADER([utility], [UTILITY])
+RB_CHK_SYSHEADER([functional], [FUNCTIONAL])
+RB_CHK_SYSHEADER([algorithm], [ALGORITHM])
+RB_CHK_SYSHEADER([numeric], [NUMERIC])
+RB_CHK_SYSHEADER([cmath], [CMATH])
+RB_CHK_SYSHEADER([memory], [MEMORY])
+RB_CHK_SYSHEADER([exception], [EXCEPTION])
+RB_CHK_SYSHEADER([cerrno], [CERRNO])
+RB_CHK_SYSHEADER([system_error], [SYSTEM_ERROR])
+RB_CHK_SYSHEADER([map], [MAP])
+RB_CHK_SYSHEADER([set], [SET])
+RB_CHK_SYSHEADER([list], [LIST])
+RB_CHK_SYSHEADER([stack], [STACK])
+RB_CHK_SYSHEADER([queue], [QUEUE])
+RB_CHK_SYSHEADER([deque], [DEQUE])
+RB_CHK_SYSHEADER([array], [ARRAY])
+RB_CHK_SYSHEADER([vector], [VECTOR])
+RB_CHK_SYSHEADER([forward_list], [FORWARD_LIST])
+RB_CHK_SYSHEADER([unordered_map], [UNORDERED_MAP])
+RB_CHK_SYSHEADER([string], [STRING])
+RB_CHK_SYSHEADER([cstring], [CSTRING])
+RB_CHK_SYSHEADER([locale], [LOCALE])
+RB_CHK_SYSHEADER([codecvt], [CODECVT])
+RB_CHK_SYSHEADER([sstream], [SSTREAM])
+RB_CHK_SYSHEADER([fstream], [FSTREAM])
+RB_CHK_SYSHEADER([iostream], [IOSTREAM])
+RB_CHK_SYSHEADER([iomanip], [IOMANIP])
+RB_CHK_SYSHEADER([cstdio], [CSTDIO])
+RB_CHK_SYSHEADER([chrono], [CHRONO])
+RB_CHK_SYSHEADER([ctime], [CTIME])
+RB_CHK_SYSHEADER([atomic], [ATOMIC])
+RB_CHK_SYSHEADER([thread], [THREAD])
+RB_CHK_SYSHEADER([mutex], [MUTEX])
+RB_CHK_SYSHEADER([shared_mutex], [SHARED_MUTEX])
 RB_CHK_SYSHEADER([condition_variable], [CONDITION_VARIABLE])
-RB_CHK_SYSHEADER([random],         [RANDOM])
-RB_CHK_SYSHEADER([bitset],         [BITSET])
+RB_CHK_SYSHEADER([random], [RANDOM])
+RB_CHK_SYSHEADER([bitset], [BITSET])
+RB_CHK_SYSHEADER([string_view], [STRING_VIEW])
+
+dnl windows platform
+RB_CHK_SYSHEADER([windows.h], [WINDOWS_H])
+RB_CHK_SYSHEADER([winsock2.h], [WINSOCK2_H])
+RB_CHK_SYSHEADER([ws2tcpip.h], [WS2TCPIP_H])
+RB_CHK_SYSHEADER([iphlpapi.h], [IPHLPAPI_H])
 
 dnl experimental
-RB_CHK_SYSHEADER([string_view],                 [STRING_VIEW])
-RB_CHK_SYSHEADER([experimental/string_view],    [EXPERIMENTAL_STRING_VIEW])
-
-RB_CHK_SYSHEADER([windows.h],      [WINDOWS_H])
-RB_CHK_SYSHEADER([winsock2.h],     [WINSOCK2_H])
-RB_CHK_SYSHEADER([ws2tcpip.h],     [WS2TCPIP_H])
-RB_CHK_SYSHEADER([iphlpapi.h],     [IPHLPAPI_H])
+RB_CHK_SYSHEADER([experimental/string_view], [EXPERIMENTAL_STRING_VIEW])
 
 
 dnl