diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 40fc5e633992036a2c06867857a681792178ef00..2c6ccce7cb5dc32097d24514ee525729efb6b7ff 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -7262,9 +7262,9 @@ aarch64_vfp_is_call_candidate (cumulative_args_t pcum_v, machine_mode mode,
 /* Given MODE and TYPE of a function argument, return the alignment in
    bits.  The idea is to suppress any stronger alignment requested by
    the user and opt for the natural alignment (specified in AAPCS64 \S
-   4.1).  ABI_BREAK is set to true if the alignment was incorrectly
-   calculated in versions of GCC prior to GCC-9.  This is a helper
-   function for local use only.  */
+   4.1).  ABI_BREAK is set to the old alignment if the alignment was
+   incorrectly calculated in versions of GCC prior to GCC-9.  This is
+   a helper function for local use only.  */
 
 static unsigned int
 aarch64_function_arg_alignment (machine_mode mode, const_tree type,
@@ -7304,7 +7304,10 @@ aarch64_function_arg_alignment (machine_mode mode, const_tree type,
 	   "s" contains only one Fundamental Data Type (the int field)
 	   but gains 8-byte alignment and size thanks to "e".  */
 	alignment = std::max (alignment, DECL_ALIGN (field));
-	if (DECL_BIT_FIELD_TYPE (field))
+
+	/* Take bit-field type's alignment into account only if the
+	   user didn't override this field's alignment.  */
+	if (DECL_BIT_FIELD_TYPE (field) && !DECL_USER_ALIGN (field))
 	  bitfield_alignment
 	    = std::max (bitfield_alignment,
 			TYPE_ALIGN (DECL_BIT_FIELD_TYPE (field)));
diff --git a/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c b/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c
new file mode 100644
index 0000000000000000000000000000000000000000..24895c3ab48309b601f6f22c176f1e52350c2257
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c
@@ -0,0 +1,105 @@
+/* Test AAPCS64 layout and __builtin_va_arg.
+
+   This test covers a corner case where a composite type parameter fits in one
+   register: we do not need a double-word alignment when accessing it in the
+   va_arg stack area.  */
+
+/* { dg-do run { target aarch64*-*-* } } */
+
+#ifndef IN_FRAMEWORK
+#define AAPCS64_TEST_STDARG
+#define TESTFILE "va_arg-17.c"
+#include "type-def.h"
+
+enum E6 { e6_0, e6_1, e6_2, e6_3, e6_65533 = 65533, e6_65534, e6_65535 };
+typedef enum E6 Tal16E6 __attribute__((aligned (16)));
+typedef unsigned int Tuint;
+
+int fails;
+
+union S2844 {
+  Tuint a:((((10) - 1) & 31) + 1);
+  Tal16E6 __attribute__((aligned (2), packed)) b:31;
+  struct{}c[0];
+} ;
+union S2844 s2844;
+union S2844 a2844[5];
+
+#define HAS_DATA_INIT_FUNC
+void init_data ()
+{
+  memset (&s2844, '\0', sizeof (s2844));
+  memset (a2844, '\0', sizeof (a2844));
+  s2844.a = 799U;
+  a2844[2].a = 586U;
+}
+
+#include "abitest.h"
+#else
+  ARG       (int          , 1        , W0 , LAST_NAMED_ARG_ID)
+  DOTS
+  ANON_PROMOTED  (float   , 1.0f, double, 1.0, D0, 1)
+  ANON      (union S2844  , s2844    , X1 , 2)
+  ANON      (long long    , 2LL      , X2 , 3)
+  ANON      (union  S2844 , a2844[2] , X3 , 4)
+  LAST_ANON (union  S2844 , a2844[2] , X4 , 5)
+#endif
+
+#if 0
+  /* This test is derived from a case generated by struct-layout-1.exp:  */
+
+enum E6 { e6_0, e6_1, e6_2, e6_3, e6_65533 = 65533, e6_65534, e6_65535 };
+typedef enum E6 Tal16E6 __attribute__((aligned (16)));
+typedef unsigned int Tuint;
+
+int fails;
+
+union S2844 {
+  Tuint a:((((10) - 1) & 31) + 1);
+  Tal16E6 __attribute__((aligned (2), packed)) b:31;
+  struct{}c[0];
+} ;
+union S2844 s2844;
+union S2844 a2844[5];
+
+typedef __builtin_va_list __gnuc_va_list;
+typedef __gnuc_va_list va_list;
+
+void check2844va (int z, ...) {
+  union S2844 arg, *p;
+  va_list ap;
+
+  __builtin_va_start(ap,z);
+  if (__builtin_va_arg(ap,double) != 1.0)
+    printf ("fail %d.%d\n", 2844, 0), ++fails;
+
+  p = &s2844;
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 1), ++fails;
+
+  if (__builtin_va_arg(ap,long long) != 3LL)
+    printf ("fail %d.%d\n", 2844, 2), ++fails;
+
+  p = &a2844[2];
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 3), ++fails;
+
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 4), ++fails;
+
+  __builtin_va_end(ap);
+}
+
+int main (void) {
+  int i, j;
+  memset (&s2844, '\0', sizeof (s2844));
+  memset (a2844, '\0', sizeof (a2844));
+  s2844.a = 799U;
+  a2844[2].a = 586U;
+  check2844va (1, 1.0, s2844, 2LL, a2844[2], a2844[2]);
+  exit (fails != 0);
+}
+#endif /* 0 */
diff --git a/gcc/testsuite/gcc.target/aarch64/pr105549.c b/gcc/testsuite/gcc.target/aarch64/pr105549.c
new file mode 100644
index 0000000000000000000000000000000000000000..55a91ed6bc48b56eed61d668971e890dbd3250ef
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr105549.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-save-temps" } */
+
+enum e { E1 };
+typedef enum e e __attribute__((aligned(16)));
+union u {
+    __attribute__((aligned(2), packed)) e a : 1;
+    int x[4];
+};
+union u g(int a, union u u2) { return u2; }
+
+/* { dg-final { scan-assembler "stp\tx1, x2, \\\[sp, 8\\\]" } } */