diff --git a/Misc/NEWS.d/next/Build/2019-09-28-02-37-11.bpo-38301.123456.rst b/Misc/NEWS.d/next/Build/2019-09-28-02-37-11.bpo-38301.123456.rst
new file mode 100644
index 00000000000..59c9a76385e
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2019-09-28-02-37-11.bpo-38301.123456.rst
@@ -0,0 +1,2 @@
+In Solaris family, we must be sure to use ``-D_REENTRANT``.
+Patch by Jesús Cea Avión.
diff --git a/configure b/configure
index bb8fbc26c74..f1979c1b812 100755
--- a/configure
+++ b/configure
@@ -10500,6 +10500,9 @@ then
     $as_echo "#define _REENTRANT 1" >>confdefs.h
 
     posix_threads=yes
+    if test "$ac_sys_system" = "SunOS"; then
+        CFLAGS="$CFLAGS -D_REENTRANT"
+    fi
 elif test "$ac_cv_kpthread" = "yes"
 then
     CC="$CC -Kpthread"
diff --git a/configure.ac b/configure.ac
index 69e2a5ea556..917a9087185 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3063,6 +3063,9 @@ then
     # Defining _REENTRANT on system with POSIX threads should not hurt.
     AC_DEFINE(_REENTRANT)
     posix_threads=yes
+    if test "$ac_sys_system" = "SunOS"; then
+        CFLAGS="$CFLAGS -D_REENTRANT"
+    fi
 elif test "$ac_cv_kpthread" = "yes"
 then
     CC="$CC -Kpthread"