diff --git a/libatomic/Makefile.in b/libatomic/Makefile.in
index 5a13bc6dfb0..dc2330b91fd 100644
--- a/libatomic/Makefile.in
+++ b/libatomic/Makefile.in
@@ -328,6 +328,7 @@ SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 SIZES = @SIZES@
 STRIP = @STRIP@
+SYSROOT_CFLAGS_FOR_TARGET = @SYSROOT_CFLAGS_FOR_TARGET@
 VERSION = @VERSION@
 XCFLAGS = @XCFLAGS@
 XLDFLAGS = @XLDFLAGS@
diff --git a/libatomic/configure b/libatomic/configure
index dc5f4bca65e..d579bab96f8 100755
--- a/libatomic/configure
+++ b/libatomic/configure
@@ -656,6 +656,7 @@ LIBAT_BUILD_VERSIONED_SHLIB_FALSE
 LIBAT_BUILD_VERSIONED_SHLIB_TRUE
 OPT_LDFLAGS
 SECTION_LDFLAGS
+SYSROOT_CFLAGS_FOR_TARGET
 enable_aarch64_lse
 libtool_VERSION
 ENABLE_DARWIN_AT_RPATH_FALSE
@@ -11455,7 +11456,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11458 "configure"
+#line 11459 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11561,7 +11562,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11564 "configure"
+#line 11565 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11928,6 +11929,8 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
     ;;
 esac
 
+
+
 # Get target configury.
 . ${srcdir}/configure.tgt
 if test -n "$UNSUPPORTED"; then
diff --git a/libatomic/configure.ac b/libatomic/configure.ac
index 6919d212ae5..5f2821ac3f4 100644
--- a/libatomic/configure.ac
+++ b/libatomic/configure.ac
@@ -172,6 +172,8 @@ case "$target" in
     ;;
 esac
 
+AC_SUBST(SYSROOT_CFLAGS_FOR_TARGET)
+
 # Get target configury.
 . ${srcdir}/configure.tgt
 if test -n "$UNSUPPORTED"; then
diff --git a/libatomic/testsuite/Makefile.in b/libatomic/testsuite/Makefile.in
index b874ac527a9..247268f1949 100644
--- a/libatomic/testsuite/Makefile.in
+++ b/libatomic/testsuite/Makefile.in
@@ -198,6 +198,7 @@ SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 SIZES = @SIZES@
 STRIP = @STRIP@
+SYSROOT_CFLAGS_FOR_TARGET = @SYSROOT_CFLAGS_FOR_TARGET@
 VERSION = @VERSION@
 XCFLAGS = @XCFLAGS@
 XLDFLAGS = @XLDFLAGS@
diff --git a/libatomic/testsuite/lib/libatomic.exp b/libatomic/testsuite/lib/libatomic.exp
index c6d645e9ae3..432a67e12e9 100644
--- a/libatomic/testsuite/lib/libatomic.exp
+++ b/libatomic/testsuite/lib/libatomic.exp
@@ -146,6 +146,11 @@ proc libatomic_init { args } {
 
     set ALWAYS_CFLAGS ""
     if { $blddir != "" } {
+	# If '--with-build-sysroot=[...]' was specified, use it for build-tree
+	# testing.
+	global SYSROOT_CFLAGS_FOR_TARGET
+	lappend ALWAYS_CFLAGS "additional_flags=${SYSROOT_CFLAGS_FOR_TARGET}"
+
 	lappend ALWAYS_CFLAGS "additional_flags=-B${blddir}/"
 	lappend ALWAYS_CFLAGS "additional_flags=-I${blddir}"
         if [istarget *-*-darwin*] {
diff --git a/libatomic/testsuite/libatomic-site-extra.exp.in b/libatomic/testsuite/libatomic-site-extra.exp.in
index c0d26660bad..5c81b7750bb 100644
--- a/libatomic/testsuite/libatomic-site-extra.exp.in
+++ b/libatomic/testsuite/libatomic-site-extra.exp.in
@@ -1 +1 @@
-set GCC_UNDER_TEST {@CC@}
+set SYSROOT_CFLAGS_FOR_TARGET {@SYSROOT_CFLAGS_FOR_TARGET@}