diff --git a/ChangeLog b/ChangeLog
index c11418b7a..50e78f9a4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2008-08-11  Werner Koch  <wk@g10code.com>
+
+	* configure.ac: Check for size of time_t.
+
 2008-04-01  Werner Koch  <wk@g10code.com>
 
 	* configure.ac (AC_INIT): Fix quoting.
diff --git a/configure.ac b/configure.ac
index f4c8bebe7..19afbaedb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -949,6 +949,19 @@ AC_CHECK_SIZEOF(unsigned short)
 AC_CHECK_SIZEOF(unsigned int)
 AC_CHECK_SIZEOF(unsigned long)
 AC_CHECK_SIZEOF(unsigned long long)
+AC_CHECK_SIZEOF(time_t,,[[
+#include <stdio.h>
+#if TIME_WITH_SYS_TIME
+# include <sys/time.h>
+# include <time.h>
+#else
+# if HAVE_SYS_TIME_H
+#  include <sys/time.h>
+# else
+#  include <time.h>
+# endif
+#endif
+]])
 
 # Ensure that we have UINT64_C before we bother to check for uint64_t
 AC_CHECK_HEADERS([inttypes.h])
diff --git a/g10/ChangeLog b/g10/ChangeLog
index b8f338b8f..0d9ba8c9c 100644
--- a/g10/ChangeLog
+++ b/g10/ChangeLog
@@ -1,3 +1,8 @@
+2008-08-11  Werner Koch  <wk@g10code.com>
+
+	* keygen.c (ask_expire_interval): Check for time overflow of an
+	u32.  Fixes bug #947.  Use SIZEOF_TIME_T for the 2039--2106 check.
+
 2008-08-01  Werner Koch  <wk@g10code.com>
 
 	* tdbio.c (open_db) [!EROFS]: Move closing parens out of the
diff --git a/g10/keygen.c b/g10/keygen.c
index a74c9a2f2..9bc18777e 100644
--- a/g10/keygen.c
+++ b/g10/keygen.c
@@ -1697,12 +1697,18 @@ ask_expire_interval(u32 timestamp,int object,const char *def_expire)
 		       ? _("Key expires at %s\n")
 		       : _("Signature expires at %s\n"),
 		       asctimestamp((ulong)(timestamp + interval) ) );
-	    /* FIXME: This check yields warning on alhas: Write a
-	       configure check and to this check here only for 32 bit
-	       machines */
-	    if( (time_t)((ulong)(timestamp+interval)) < 0 )
-	      tty_printf(_("Your system can't display dates beyond 2038.\n"
-			   "However, it will be correctly handled up to 2106.\n"));
+#if SIZEOF_TIME_T <= 4
+	    if ((time_t)((ulong)(timestamp+interval)) < 0 )
+	      tty_printf (_("Your system can't display dates beyond 2038.\n"
+                            "However, it will be correctly handled up to"
+                            " 2106.\n"));
+            else
+#endif /*SIZEOF_TIME_T*/
+              if ( (time_t)((unsigned long)(timestamp+interval)) < timestamp )
+                {
+                  tty_printf (_("invalid value\n"));
+                  continue;
+                }
 	  }
 
 	if( cpr_enabled() || cpr_get_answer_is_yes("keygen.valid.okay",