diff --git a/sys/x86/include/bus.h b/sys/x86/include/bus.h
index fb5babf43268..52c4251b931c 100644
--- a/sys/x86/include/bus.h
+++ b/sys/x86/include/bus.h
@@ -130,6 +130,7 @@
 #define BUS_SPACE_MAXADDR	0xFFFFFFFF
 #endif
 
+#define BUS_SPACE_INVALID_DATA	(~0)
 #define BUS_SPACE_UNRESTRICTED	(~0)
 
 /*
@@ -221,6 +222,12 @@ static __inline u_int32_t bus_space_read_4(bus_space_tag_t tag,
 					   bus_space_handle_t handle,
 					   bus_size_t offset);
 
+#ifdef __amd64__
+static __inline uint64_t bus_space_read_8(bus_space_tag_t tag,
+					  bus_space_handle_t handle,
+					  bus_size_t offset);
+#endif
+
 static __inline u_int8_t
 bus_space_read_1(bus_space_tag_t tag, bus_space_handle_t handle,
 		 bus_size_t offset)
@@ -251,8 +258,16 @@ bus_space_read_4(bus_space_tag_t tag, bus_space_handle_t handle,
 	return (*(volatile u_int32_t *)(handle + offset));
 }
 
-#if 0	/* Cause a link error for bus_space_read_8 */
-#define	bus_space_read_8(t, h, o)	!!! bus_space_read_8 unimplemented !!!
+#ifdef __amd64__
+static __inline uint64_t
+bus_space_read_8(bus_space_tag_t tag, bus_space_handle_t handle,
+		 bus_size_t offset)
+{
+
+	if (tag == X86_BUS_SPACE_IO) /* No 8 byte IO space access on x86 */
+		return (BUS_SPACE_INVALID_DATA);
+	return (*(volatile uint64_t *)(handle + offset));
+}
 #endif
 
 /*
@@ -479,6 +494,12 @@ static __inline void bus_space_write_4(bus_space_tag_t tag,
 				       bus_space_handle_t bsh,
 				       bus_size_t offset, u_int32_t value);
 
+#ifdef __amd64__
+static __inline void bus_space_write_8(bus_space_tag_t tag,
+				       bus_space_handle_t bsh,
+				       bus_size_t offset, uint64_t value);
+#endif
+
 static __inline void
 bus_space_write_1(bus_space_tag_t tag, bus_space_handle_t bsh,
 		       bus_size_t offset, u_int8_t value)
@@ -512,8 +533,17 @@ bus_space_write_4(bus_space_tag_t tag, bus_space_handle_t bsh,
 		*(volatile u_int32_t *)(bsh + offset) = value;
 }
 
-#if 0	/* Cause a link error for bus_space_write_8 */
-#define	bus_space_write_8	!!! bus_space_write_8 not implemented !!!
+#ifdef __amd64__
+static __inline void
+bus_space_write_8(bus_space_tag_t tag, bus_space_handle_t bsh,
+		  bus_size_t offset, uint64_t value)
+{
+
+	if (tag == X86_BUS_SPACE_IO) /* No 8 byte IO space access on x86 */
+		return;
+	else
+		*(volatile uint64_t *)(bsh + offset) = value;
+}
 #endif
 
 /*