diff --git a/src/x86_64/ucontext_i.h b/src/x86_64/ucontext_i.h
index 459c56a2..2724bc0b 100644
--- a/src/x86_64/ucontext_i.h
+++ b/src/x86_64/ucontext_i.h
@@ -22,6 +22,7 @@ LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 
+#if defined __linux__
 #define UC_MCONTEXT_GREGS_R8	0x28
 #define UC_MCONTEXT_GREGS_R9	0x30
 #define UC_MCONTEXT_GREGS_R10	0x38
@@ -42,3 +43,25 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 #define UC_MCONTEXT_FPREGS_PTR  0x1a8
 #define UC_MCONTEXT_FPREGS_MEM	0xe0
 #define FPREGS_OFFSET_MXCSR	0x18
+#elif defined __FreeBSD__
+#define UC_MCONTEXT_GREGS_R8	0x38
+#define UC_MCONTEXT_GREGS_R9	0x40
+#define UC_MCONTEXT_GREGS_R10	0x60
+#define UC_MCONTEXT_GREGS_R11	0x68
+#define UC_MCONTEXT_GREGS_R12	0x70
+#define UC_MCONTEXT_GREGS_R13	0x78
+#define UC_MCONTEXT_GREGS_R14	0x80
+#define UC_MCONTEXT_GREGS_R15	0x88
+#define UC_MCONTEXT_GREGS_RDI	0x18
+#define UC_MCONTEXT_GREGS_RSI	0x20
+#define UC_MCONTEXT_GREGS_RBP	0x58
+#define UC_MCONTEXT_GREGS_RBX	0x50
+#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_RIP	0xb0
+#define UC_MCONTEXT_FPREGS_PTR  0x1a8 /* XXXKIB */
+#define UC_MCONTEXT_FPREGS_MEM	0xe0  /* XXXKIB */
+#define FPREGS_OFFSET_MXCSR	0x18  /* XXXKIB */
+#endif