diff --git a/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst b/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst
new file mode 100644
index 00000000000000..7dafc105c45ea9
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2020-12-13-14-43-10.bpo-42598.7ipr5H.rst
@@ -0,0 +1,2 @@
+Fix implicit function declarations in configure which could have resulted in
+incorrect configuration checks.  Patch contributed by Joshua Root.
diff --git a/configure b/configure
index dfb6e7ef3f0f79..15ea8cdfdc0f06 100755
--- a/configure
+++ b/configure
@@ -10928,10 +10928,10 @@ else
       main() {
         pthread_attr_t attr;
         pthread_t id;
-        if (pthread_attr_init(&attr)) exit(-1);
-        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) exit(-1);
-        if (pthread_create(&id, &attr, foo, NULL)) exit(-1);
-        exit(0);
+        if (pthread_attr_init(&attr)) return (-1);
+        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
+        if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        return (0);
       }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :
@@ -14916,7 +14916,7 @@ else
   int main()
   {
 	/* Success: exit code 0 */
-        exit((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
+        return ((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
   }
 
 _ACEOF
@@ -15261,7 +15261,7 @@ else
 
 int main()
 {
-	exit(((-1)>>3 == -1) ? 0 : 1);
+	return (((-1)>>3 == -1) ? 0 : 1);
 }
 
 _ACEOF
@@ -15731,6 +15731,7 @@ else
 /* end confdefs.h.  */
 
 #include <poll.h>
+#include <unistd.h>
 
 int main()
 {
diff --git a/configure.ac b/configure.ac
index 6c8fd5a3892778..c93ba0ee7dc0e0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3210,10 +3210,10 @@ if test "$posix_threads" = "yes"; then
       main() {
         pthread_attr_t attr;
         pthread_t id;
-        if (pthread_attr_init(&attr)) exit(-1);
-        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) exit(-1);
-        if (pthread_create(&id, &attr, foo, NULL)) exit(-1);
-        exit(0);
+        if (pthread_attr_init(&attr)) return (-1);
+        if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
+        if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        return (0);
       }]])],
       [ac_cv_pthread_system_supported=yes],
       [ac_cv_pthread_system_supported=no],
@@ -4616,7 +4616,7 @@ then
   int main()
   {
 	/* Success: exit code 0 */
-        exit((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
+        return ((((wchar_t) -1) < ((wchar_t) 0)) ? 0 : 1);
   }
   ]])],
   [ac_cv_wchar_t_signed=yes],
@@ -4709,7 +4709,7 @@ AC_CACHE_VAL(ac_cv_rshift_extends_sign, [
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
 int main()
 {
-	exit(((-1)>>3 == -1) ? 0 : 1);
+	return (((-1)>>3 == -1) ? 0 : 1);
 }
 ]])],
 [ac_cv_rshift_extends_sign=yes],
@@ -4856,6 +4856,7 @@ AC_MSG_CHECKING(for broken poll())
 AC_CACHE_VAL(ac_cv_broken_poll,
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <poll.h>
+#include <unistd.h>
 
 int main()
 {