diff --git a/src/x86_64/Gis_signal_frame.c b/src/x86_64/Gis_signal_frame.c
index 3bee93a8..263ad87a 100644
--- a/src/x86_64/Gis_signal_frame.c
+++ b/src/x86_64/Gis_signal_frame.c
@@ -97,6 +97,10 @@ eb fd			jmp	0b
       || (ret = (*a->access_mem) (as, ip + 8, &w1, 0, arg)) < 0
       || (ret = (*a->access_mem) (as, ip + 16, &w2, 0, arg)) < 0)
     return 0;
+#if 0
+  fprintf(stderr, "is_signal_frame: ip %lx w0 %lx w1 %lx w2 %lx\n",
+	  ip, w0, w1, w2);
+#endif
   w2 &= 0xffffff;
   return (w0 == 0x48006a10247c8d48 &&
 	  w1 == 0x050f000001a1c0c7 &&
diff --git a/src/x86_64/ucontext_i.h b/src/x86_64/ucontext_i.h
index c942080b..82114dd2 100644
--- a/src/x86_64/ucontext_i.h
+++ b/src/x86_64/ucontext_i.h
@@ -59,7 +59,7 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 #define UC_MCONTEXT_GREGS_RDX	0x28
 #define UC_MCONTEXT_GREGS_RAX	0x48
 #define UC_MCONTEXT_GREGS_RCX	0x30
-#define UC_MCONTEXT_GREGS_RSP	0xa0
+#define UC_MCONTEXT_GREGS_RSP	0xc8
 #define UC_MCONTEXT_GREGS_RIP	0xb0
 #define UC_MCONTEXT_FPSTATE	0xf0
 #define UC_MCONTEXT_OWNEDFP	0xe8