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 00000000000000..59c9a76385e2bd
--- /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 e39c16eee2b903..c34a13fb585af7 100755
--- a/configure
+++ b/configure
@@ -10406,6 +10406,9 @@ then
 
     posix_threads=yes
     THREADOBJ="Python/thread.o"
+    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 cf280506bd011f..3741c06e08f7f7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3056,6 +3056,9 @@ then
     AC_DEFINE(_REENTRANT)
     posix_threads=yes
     THREADOBJ="Python/thread.o"
+    if test "$ac_sys_system" = "SunOS"; then
+        CFLAGS="$CFLAGS -D_REENTRANT"
+    fi
 elif test "$ac_cv_kpthread" = "yes"
 then
     CC="$CC -Kpthread"