diff --git a/doc/guides/rel_notes/release_21_05.rst b/doc/guides/rel_notes/release_21_05.rst
index 5aa9ed7db..f606186ec 100644
--- a/doc/guides/rel_notes/release_21_05.rst
+++ b/doc/guides/rel_notes/release_21_05.rst
@@ -84,6 +84,9 @@ API Changes
    Also, make sure to start the actual text at the margin.
    =======================================================
 
+* eal/windows: Removed POSIX symbol export from ``<rte_os.h>``.
+  It has been incorrect and could conflict with consumer POSIX implementations.
+
 
 ABI Changes
 -----------
diff --git a/lib/librte_cmdline/cmdline.c b/lib/librte_cmdline/cmdline.c
index 79ea5f98c..49770869b 100644
--- a/lib/librte_cmdline/cmdline.c
+++ b/lib/librte_cmdline/cmdline.c
@@ -18,10 +18,6 @@
 
 #include "cmdline_private.h"
 
-#ifdef RTE_EXEC_ENV_WINDOWS
-#define write _write
-#endif
-
 static void
 cmdline_valid_buffer(struct rdline *rdl, const char *buf,
 		     __rte_unused unsigned int size)
diff --git a/lib/librte_cmdline/cmdline_socket.c b/lib/librte_cmdline/cmdline_socket.c
index 0fe149700..998e8ade2 100644
--- a/lib/librte_cmdline/cmdline_socket.c
+++ b/lib/librte_cmdline/cmdline_socket.c
@@ -16,10 +16,6 @@
 #include "cmdline_private.h"
 #include "cmdline_socket.h"
 
-#ifdef RTE_EXEC_ENV_WINDOWS
-#define open _open
-#endif
-
 struct cmdline *
 cmdline_file_new(cmdline_parse_ctx_t *ctx, const char *prompt, const char *path)
 {
diff --git a/lib/librte_eal/common/eal_common_errno.c b/lib/librte_eal/common/eal_common_errno.c
index 2a10fb823..f86802705 100644
--- a/lib/librte_eal/common/eal_common_errno.c
+++ b/lib/librte_eal/common/eal_common_errno.c
@@ -15,6 +15,10 @@
 #include <rte_errno.h>
 #include <rte_string_fns.h>
 
+#ifdef RTE_EXEC_ENV_WINDOWS
+#define strerror_r(errnum, buf, buflen) strerror_s(buf, buflen, errnum)
+#endif
+
 RTE_DEFINE_PER_LCORE(int, _rte_errno);
 
 const char *
diff --git a/lib/librte_eal/common/eal_common_options.c b/lib/librte_eal/common/eal_common_options.c
index 230bac9f3..6d4d6ff19 100644
--- a/lib/librte_eal/common/eal_common_options.c
+++ b/lib/librte_eal/common/eal_common_options.c
@@ -1936,7 +1936,7 @@ eal_check_common_options(struct internal_config *internal_cfg)
 		RTE_LOG(ERR, EAL, "Invalid length of --" OPT_MBUF_POOL_OPS_NAME" option\n");
 		return -1;
 	}
-	if (index(eal_get_hugefile_prefix(), '%') != NULL) {
+	if (strchr(eal_get_hugefile_prefix(), '%') != NULL) {
 		RTE_LOG(ERR, EAL, "Invalid char, '%%', in --"OPT_FILE_PREFIX" "
 			"option\n");
 		return -1;
diff --git a/lib/librte_eal/windows/include/rte_os.h b/lib/librte_eal/windows/include/rte_os.h
index 7ef38ff06..d97e07890 100644
--- a/lib/librte_eal/windows/include/rte_os.h
+++ b/lib/librte_eal/windows/include/rte_os.h
@@ -11,7 +11,6 @@
  * Windows OS. It must not include Windows-specific headers.
  */
 
-#include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -20,100 +19,36 @@
 extern "C" {
 #endif
 
-/* limits.h replacement, value as in <windows.h> */
-#ifndef PATH_MAX
-#define PATH_MAX _MAX_PATH
-#endif
-
-#ifndef sleep
-#define sleep(x) Sleep(1000 * (x))
-#endif
-
-#ifndef strerror_r
-#define strerror_r(a, b, c) strerror_s(b, c, a)
-#endif
-
-#ifndef strdup
-/* strdup is deprecated in Microsoft libc and _strdup is preferred */
-#define strdup(str) _strdup(str)
-#endif
-
-#ifndef strtok_r
-#define strtok_r(str, delim, saveptr) strtok_s(str, delim, saveptr)
-#endif
-
-#ifndef index
-#define index(a, b)     strchr(a, b)
-#endif
-
-#ifndef rindex
-#define rindex(a, b)    strrchr(a, b)
-#endif
-
-#ifndef strncasecmp
-#define strncasecmp(s1, s2, count)        _strnicmp(s1, s2, count)
-#endif
-
-#ifndef close
-#define close _close
-#endif
-
-#ifndef unlink
-#define unlink _unlink
-#endif
-
 /* cpu_set macros implementation */
 #define RTE_CPU_AND(dst, src1, src2) CPU_AND(dst, src1, src2)
 #define RTE_CPU_OR(dst, src1, src2) CPU_OR(dst, src1, src2)
 #define RTE_CPU_FILL(set) CPU_FILL(set)
 #define RTE_CPU_NOT(dst, src) CPU_NOT(dst, src)
 
-/* as in <windows.h> */
-typedef long long ssize_t;
-
-#ifndef RTE_TOOLCHAIN_GCC
-
-static inline int
-asprintf(char **buffer, const char *format, ...)
-{
-	int size, ret;
-	va_list arg;
-
-	va_start(arg, format);
-	size = vsnprintf(NULL, 0, format, arg);
-	va_end(arg);
-	if (size < 0)
-		return -1;
-	size++;
+/* Allow DPDK to call common functions by POSIX names. */
+#ifdef RTE_BUILD_INTERNAL
 
-	*buffer = (char *)malloc(size);
-	if (*buffer == NULL)
-		return -1;
-
-	va_start(arg, format);
-	ret = vsnprintf(*buffer, size, format, arg);
-	va_end(arg);
-	if (ret != size - 1) {
-		free(*buffer);
-		return -1;
-	}
-	return ret;
-}
+#ifndef PATH_MAX
+#define PATH_MAX _MAX_PATH
+#endif
 
-static inline const char *
-eal_strerror(int code)
-{
-	static char buffer[128];
+#define strdup(str) _strdup(str)
+#define strtok_r(str, delim, saveptr) strtok_s(str, delim, saveptr)
+#define strncasecmp(s1, s2, count) _strnicmp(s1, s2, count)
 
-	strerror_s(buffer, sizeof(buffer), code);
-	return buffer;
-}
+#define open(path, flags, ...) _open(path, flags, ##__VA_ARGS__)
+#define read(fd, buf, n) _read(fd, buf, n)
+#define write(fd, buf, n) _write(fd, buf, n)
+#define close(fd) _close(fd)
+#define unlink(path) _unlink(path)
 
-#ifndef strerror
-#define strerror eal_strerror
-#endif
+#endif /* RTE_BUILD_INTERNAL */
 
-#endif /* RTE_TOOLCHAIN_GCC */
+/* This is an exception without "rte_" prefix, because Windows does have
+ * ssize_t, but it's defined in <windows.h> which we avoid to expose.
+ * If ssize_t is defined in user code, it necessarily has the same type.
+ */
+typedef long long ssize_t;
 
 #ifdef __cplusplus
 }
