diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
index 0c27f90d29..b32a5e3528 100644
--- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
@@ -79,15 +79,15 @@
 ENTRY (STRCMP)
 # ifdef USE_AS_STRNCMP
 	/* Check for simple cases (0 or 1) in offset.  */
-	cmp	$1, %rdx
+	cmp	$1, %RDX_LP
 	je	L(char0)
 	jb	L(zero)
 #  ifdef USE_AS_WCSCMP
 	/* Convert units: from wide to byte char.  */
-	shl	$2, %rdx
+	shl	$2, %RDX_LP
 #  endif
 	/* Register %r11 tracks the maximum offset.  */
-	movq	%rdx, %r11
+	mov	%RDX_LP, %R11_LP
 # endif
 	movl	%edi, %eax
 	xorl	%edx, %edx
diff --git a/sysdeps/x86_64/multiarch/strcmp-sse42.S b/sysdeps/x86_64/multiarch/strcmp-sse42.S
index 2f4b34a03f..73bbe5c9e1 100644
--- a/sysdeps/x86_64/multiarch/strcmp-sse42.S
+++ b/sysdeps/x86_64/multiarch/strcmp-sse42.S
@@ -156,11 +156,11 @@ STRCMP_SSE42:
 #endif
 
 #if defined USE_AS_STRNCMP || defined USE_AS_STRNCASECMP_L
-	test	%rdx, %rdx
+	test	%RDX_LP, %RDX_LP
 	je	LABEL(strcmp_exitz)
-	cmp	$1, %rdx
+	cmp	$1, %RDX_LP
 	je	LABEL(Byte0)
-	mov	%rdx, %r11
+	mov	%RDX_LP, %R11_LP
 #endif
 	mov	%esi, %ecx
 	mov	%edi, %eax
diff --git a/sysdeps/x86_64/strcmp.S b/sysdeps/x86_64/strcmp.S
index 55445148d5..f95463155a 100644
--- a/sysdeps/x86_64/strcmp.S
+++ b/sysdeps/x86_64/strcmp.S
@@ -135,11 +135,11 @@ ENTRY (STRCMP)
  * This implementation uses SSE to compare up to 16 bytes at a time.
  */
 #if defined USE_AS_STRNCMP || defined USE_AS_STRNCASECMP_L
-	test	%rdx, %rdx
+	test	%RDX_LP, %RDX_LP
 	je	LABEL(strcmp_exitz)
-	cmp	$1, %rdx
+	cmp	$1, %RDX_LP
 	je	LABEL(Byte0)
-	mov	%rdx, %r11
+	mov	%RDX_LP, %R11_LP
 #endif
 	mov	%esi, %ecx
 	mov	%edi, %eax
diff --git a/sysdeps/x86_64/x32/Makefile b/sysdeps/x86_64/x32/Makefile
index 98bd9ae9cd..db30283977 100644
--- a/sysdeps/x86_64/x32/Makefile
+++ b/sysdeps/x86_64/x32/Makefile
@@ -7,9 +7,11 @@ endif
 
 ifeq ($(subdir),string)
 tests += tst-size_t-memchr tst-size_t-memcmp tst-size_t-memcpy \
-	 tst-size_t-memrchr tst-size_t-memset
+	 tst-size_t-memrchr tst-size_t-memset tst-size_t-strncasecmp \
+	 tst-size_t-strncmp
 endif
 
 ifeq ($(subdir),wcsmbs)
-tests += tst-size_t-wmemchr tst-size_t-wmemcmp tst-size_t-wmemset
+tests += tst-size_t-wmemchr tst-size_t-wmemcmp tst-size_t-wmemset \
+	 tst-size_t-wcsncmp
 endif
diff --git a/sysdeps/x86_64/x32/tst-size_t-strncasecmp.c b/sysdeps/x86_64/x32/tst-size_t-strncasecmp.c
new file mode 100644
index 0000000000..3c2c80fd3b
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-strncasecmp.c
@@ -0,0 +1,59 @@
+/* Test strncaecmp with size_t in the lower 32 bits of 64-bit register.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define TEST_NAME "strncasecmp"
+#include "test-size_t.h"
+
+IMPL (strncasecmp, 1)
+
+typedef int (*proto_t) (const char *, const char *, size_t);
+
+static int
+__attribute__ ((noinline, noclone))
+do_strncasecmp (parameter_t a, parameter_t b)
+{
+  return CALL (b, a.p, b.p, a.len);
+}
+
+static int
+do_test (void)
+{
+  test_init ();
+
+  parameter_t dest = { { page_size }, buf1 };
+  parameter_t src = { { 0 }, buf2 };
+
+  strncpy ((char *) buf1, (const char *) buf2, page_size);
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      src.fn = impl->fn;
+      int res = do_strncasecmp (dest, src);
+      if (res)
+	{
+	  error (0, 0, "Wrong result in function %s: %i != 0",
+		 impl->name, res);
+	  ret = 1;
+	}
+    }
+
+  return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/x86_64/x32/tst-size_t-strncmp.c b/sysdeps/x86_64/x32/tst-size_t-strncmp.c
new file mode 100644
index 0000000000..bcc47c5441
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-strncmp.c
@@ -0,0 +1,78 @@
+/* Test strncmp with size_t in the lower 32 bits of 64-bit register.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifdef WIDE
+# define TEST_NAME "wcsncmp"
+#else
+# define TEST_NAME "strncmp"
+#endif
+
+#include "test-size_t.h"
+
+#ifdef WIDE
+# include <wchar.h>
+
+# define STRNCMP wcsncmp
+# define STRNCPY wcsncpy
+# define CHAR wchar_t
+#else
+# define STRNCMP strncmp
+# define STRNCPY strncpy
+# define CHAR char
+#endif
+
+IMPL (STRNCMP, 1)
+
+typedef int (*proto_t) (const CHAR *, const CHAR *, size_t);
+
+
+static int
+__attribute__ ((noinline, noclone))
+do_strncmp (parameter_t a, parameter_t b)
+{
+  return CALL (b, a.p, b.p, a.len);
+}
+
+static int
+do_test (void)
+{
+  test_init ();
+
+  size_t size = page_size / sizeof (CHAR);
+  parameter_t dest = { { size }, buf1 };
+  parameter_t src = { { 0 }, buf2 };
+
+  STRNCPY ((CHAR *) buf1, (const CHAR *) buf2, size);
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      src.fn = impl->fn;
+      int res = do_strncmp (dest, src);
+      if (res)
+	{
+	  error (0, 0, "Wrong result in function %s: %i != 0",
+		 impl->name, res);
+	  ret = 1;
+	}
+    }
+
+  return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/x86_64/x32/tst-size_t-wcsncmp.c b/sysdeps/x86_64/x32/tst-size_t-wcsncmp.c
new file mode 100644
index 0000000000..4829647c19
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-wcsncmp.c
@@ -0,0 +1,20 @@
+/* Test wcsncmp with size_t in the lower 32 bits of 64-bit register.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#define WIDE 1
+#include "tst-size_t-strncmp.c"
