diff --git a/include/endian.h b/include/endian.h
index eb25cedf0bef..87ec7866c791 100644
--- a/include/endian.h
+++ b/include/endian.h
@@ -11,9 +11,33 @@
 #ifndef _ENDIAN_H_
 #define _ENDIAN_H_
 
+/*
+ * POSIX Issue 8 requires that endian.h define uint{16,32,64}_t. Although POSIX
+ * allows stdint.h symbols here, be conservative and only define there required
+ * ones. FreeBSD's sys/_endian.h doesn't need to expose those types since it
+ * implements all the [bl]eXtoh hto[bl]eX interfaces as macros calling builtin
+ * functions. POSIX allows functions, macros or both. We opt for macros only.
+ */
+#include <sys/_types.h>
+
+#ifndef _UINT16_T_DECLARED
+typedef	__uint16_t		uint16_t;
+#define	_UINT16_T_DECLARED
+#endif
+
+#ifndef _UINT32_T_DECLARED
+typedef	__uint32_t		uint32_t;
+#define	_UINT32_T_DECLARED
+#endif
+
+#ifndef _UINT64_T_DECLARED
+typedef	__uint64_t		uint64_t;
+#define	_UINT64_T_DECLARED
+#endif
+
 /*
  * FreeBSD's sys/_endian.h is very close to the interface provided on Linux by
- * glibc's endian.h.
+ * glibc's endian.h as well as POSIX Issue 8's endian.h.
  */
 #include <sys/_endian.h>
 
diff --git a/sys/sys/_endian.h b/sys/sys/_endian.h
index 8d1eb3f3f3df..d0ffd87efa11 100644
--- a/sys/sys/_endian.h
+++ b/sys/sys/_endian.h
@@ -69,8 +69,10 @@
 
 /*
  * POSIX Issue 8 will require these for endian.h. Define them there and in the
- * traditional BSD compilation environment. Since issue 8 doesn't yet have an
- * assigned date, use strictly greater than issue 7's date.
+ * traditional BSD compilation environment. PDP_ENDIAN isn't strictly in Issue
+ * 8, but is allowed as implementations can define any *_ENDIAN symbol. Since
+ * issue 8 doesn't yet have an assigned date, use strictly greater than issue
+ * 7's date.
  */
 #if __BSD_VISIBLE || _POSIX_C_SOURCE > 200809
 #define	LITTLE_ENDIAN   _LITTLE_ENDIAN