diff --git a/libquadmath/ChangeLog b/libquadmath/ChangeLog
index 6f731ca84ad..b97a45868b3 100644
--- a/libquadmath/ChangeLog
+++ b/libquadmath/ChangeLog
@@ -1,3 +1,13 @@
+2012-11-21  Tobias Burnus  <burnus@net-b.de>
+
+	PR libquadmath/55225
+	* math/lgammaq.c (lgammaq): Use local variable if
+	math.h does not provide signgam.
+	* acinclude.m4 (LIBQUAD_CHECK_MATH_H_SIGNGAM): New check.
+	* configure.ac: Use it.
+	* configure: Regenerate.
+	* config.h.in: Regenerate.
+
 2012-11-15  Tobias Burnus  <burnus@net-b.de>
 	    Joseph Myers  <joseph@codesourcery.com>
 
diff --git a/libquadmath/acinclude.m4 b/libquadmath/acinclude.m4
index 38e0808ad93..ab73fb52e05 100644
--- a/libquadmath/acinclude.m4
+++ b/libquadmath/acinclude.m4
@@ -10,3 +10,20 @@ AC_DEFUN([AM_PROG_LIBTOOL])
 AC_DEFUN([AC_LIBTOOL_DLOPEN])
 AC_DEFUN([AC_PROG_LD])
 ])
+
+dnl Check whether POSIX's signgam is defined in math.h.
+AC_DEFUN([LIBQUAD_CHECK_MATH_H_SIGNGAM], [
+  AC_CACHE_CHECK([whether the math.h includes POSIX's signgam],
+                 libgfor_cv_have_math_h_signgam, [
+  save_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS -Werror"
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+#include <math.h>
+void foo(void) { signgam = 1; }]], [])],
+                    libgfor_cv_have_math_h_signgam=yes,
+                    libgfor_cv_have_math_h_signgam=no)
+  CFLAGS="$save_CFLAGS"])
+  if test $libgfor_cv_have_math_h_signgam = yes; then
+    AC_DEFINE(HAVE_MATH_H_SIGNGAM, 1,
+      [Define to 1 if the math.h includes POSIX's signgam.])
+  fi])
diff --git a/libquadmath/config.h.in b/libquadmath/config.h.in
index ea3f10c2786..9d18cc3ee35 100644
--- a/libquadmath/config.h.in
+++ b/libquadmath/config.h.in
@@ -45,6 +45,9 @@
 /* Define to 1 if you have the <locale.h> header file. */
 #undef HAVE_LOCALE_H
 
+/* Define to 1 if the math.h includes POSIX's signgam. */
+#undef HAVE_MATH_H_SIGNGAM
+
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
diff --git a/libquadmath/configure b/libquadmath/configure
index 16776719d01..0ea6e07455d 100755
--- a/libquadmath/configure
+++ b/libquadmath/configure
@@ -11947,6 +11947,43 @@ fi
 done
 
 
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the math.h includes POSIX's signgam" >&5
+$as_echo_n "checking whether the math.h includes POSIX's signgam... " >&6; }
+if test "${libgfor_cv_have_math_h_signgam+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+
+  save_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS -Werror"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#include <math.h>
+void foo(void) { signgam = 1; }
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libgfor_cv_have_math_h_signgam=yes
+else
+  libgfor_cv_have_math_h_signgam=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+  CFLAGS="$save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libgfor_cv_have_math_h_signgam" >&5
+$as_echo "$libgfor_cv_have_math_h_signgam" >&6; }
+  if test $libgfor_cv_have_math_h_signgam = yes; then
+
+$as_echo "#define HAVE_MATH_H_SIGNGAM 1" >>confdefs.h
+
+  fi
+
 # If available, sqrtl and cbrtl speed up the calculation -
 # but they are not required
 if test x$gcc_no_link != xyes; then
diff --git a/libquadmath/configure.ac b/libquadmath/configure.ac
index d3bfb040cd0..c547da8dc20 100644
--- a/libquadmath/configure.ac
+++ b/libquadmath/configure.ac
@@ -113,6 +113,7 @@ AC_SUBST(toolexecdir)
 AC_SUBST(toolexeclibdir)
 
 AC_CHECK_HEADERS(fenv.h langinfo.h locale.h wchar.h wctype.h limits.h ctype.h printf.h errno.h)
+LIBQUAD_CHECK_MATH_H_SIGNGAM
 
 # If available, sqrtl and cbrtl speed up the calculation -
 # but they are not required
diff --git a/libquadmath/math/lgammaq.c b/libquadmath/math/lgammaq.c
index 485939af1b4..eef62dbc91f 100644
--- a/libquadmath/math/lgammaq.c
+++ b/libquadmath/math/lgammaq.c
@@ -69,7 +69,10 @@
     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA */
 
 #include "quadmath-imp.h"
-#include <math.h>  /* For extern int signgam.  */
+
+#ifdef HAVE_MATH_H_SIGNGAM
+#include <math.h>  /* For POSIX's extern int signgam.  */
+#endif
 
 static const __float128 PIQ = 3.1415926535897932384626433832795028841972E0Q;
 static const __float128 MAXLGM = 1.0485738685148938358098967157129705071571E4928Q;
@@ -759,6 +762,9 @@ lgammaq (__float128 x)
 {
   __float128 p, q, w, z, nx;
   int i, nn;
+#ifndef HAVE_MATH_H_SIGNGAM
+  int signgam;
+#endif
 
   signgam = 1;