diff --git a/tcc.h b/tcc.h
index 7630f4cb..9b65e6d9 100644
--- a/tcc.h
+++ b/tcc.h
@@ -379,7 +379,7 @@ typedef struct SValue {
 struct Attribute {
     unsigned
         func_call     : 3, /* calling convention (0..5), see below */
-        aligned       : 5, /* alignement (0..16) */
+        aligned       : 5, /* alignment as log2+1 (0 == unspecified) */
         packed        : 1,
         func_export   : 1,
         func_import   : 1,
diff --git a/tccgen.c b/tccgen.c
index 6ea62e2e..75959adf 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -3062,6 +3062,24 @@ ST_FUNC void parse_mult_str (CString *astr, const char *msg)
     cstr_ccat(astr, '\0');
 }
 
+/* If I is >= 1 and a power of two, returns log2(i)+1.
+   If I is 0 returns 0.  */
+static int exact_log2p1(int i)
+{
+  int ret;
+  if (!i)
+    return 0;
+  for (ret = 1; i >= 1 << 8; ret += 8)
+    i >>= 8;
+  if (i >= 1 << 4)
+    ret += 4, i >>= 4;
+  if (i >= 1 << 2)
+    ret += 2, i >>= 2;
+  if (i >= 1 << 1)
+    ret++;
+  return ret;
+}
+
 /* Parse GNUC __attribute__ extension. Currently, the following
    extensions are recognized:
    - aligned(n) : set data/function alignment.
@@ -3131,7 +3149,9 @@ static void parse_attribute(AttributeDef *ad)
             } else {
                 n = MAX_ALIGN;
             }
-            ad->a.aligned = n;
+            ad->a.aligned = exact_log2p1(n);
+	    if (n != 1 << (ad->a.aligned - 1))
+	      tcc_error("alignment of %d is larger than implemented", n);
             break;
         case TOK_PACKED1:
         case TOK_PACKED2:
@@ -3270,7 +3290,7 @@ static void struct_layout(CType *type, AttributeDef *ad)
     int pcc = !tcc_state->ms_bitfields;
     Sym *f;
     if (ad->a.aligned)
-      maxalign = ad->a.aligned;
+      maxalign = 1 << (ad->a.aligned - 1);
     else
       maxalign = 1;
     offset = 0;
@@ -3293,6 +3313,8 @@ static void struct_layout(CType *type, AttributeDef *ad)
 	    align = f->r;
 	} else if (ad->a.packed || f->r == 1) {
 	    align = 1;
+	    /* Packed fields or packed records don't let the base type
+	       influence the records type alignment.  */
 	    typealign = 1;
 	} else {
 	    align = typealign;
@@ -3587,8 +3609,9 @@ static void struct_decl(CType *type, AttributeDef *ad, int u)
 		    /* Only remember non-default alignment.  */
 		    alignoverride = 0;
                     if (ad1.a.aligned) {
-                        if (align < ad1.a.aligned)
-                            alignoverride = ad1.a.aligned;
+			int speca = 1 << (ad1.a.aligned - 1);
+                        if (align < speca)
+                            alignoverride = speca;
                     } else if (ad1.a.packed || ad->a.packed) {
                         alignoverride = 1;
                     } else if (*tcc_state->pack_stack_ptr) {
@@ -6594,8 +6617,9 @@ static void decl_initializer_alloc(CType *type, AttributeDef *ad, int r,
 	        * pointed_size(&flexible_array->type);
     /* take into account specified alignment if bigger */
     if (ad->a.aligned) {
-        if (ad->a.aligned > align)
-            align = ad->a.aligned;
+	int speca = 1 << (ad->a.aligned - 1);
+        if (speca > align)
+            align = speca;
     } else if (ad->a.packed) {
         align = 1;
     }
diff --git a/tests/tcctest.c b/tests/tcctest.c
index 9fcd7a49..68f8db64 100644
--- a/tests/tcctest.c
+++ b/tests/tcctest.c
@@ -1048,6 +1048,11 @@ int pad1;
    a copy of it).
 struct aligntest7 altest7[2] __attribute__((aligned(16)));*/
 
+struct aligntest8
+{
+  int i;
+} __attribute__((aligned(4096)));
+
 struct Large {
     unsigned long flags;
     union {
@@ -1129,6 +1134,8 @@ void struct_test()
            sizeof(struct aligntest6), __alignof__(struct aligntest6));
     printf("aligntest7 sizeof=%d alignof=%d\n",
            sizeof(struct aligntest7), __alignof__(struct aligntest7));
+    printf("aligntest8 sizeof=%d alignof=%d\n",
+           sizeof(struct aligntest8), __alignof__(struct aligntest8));
     printf("altest5 sizeof=%d alignof=%d\n",
            sizeof(altest5), __alignof__(altest5));
     printf("altest6 sizeof=%d alignof=%d\n",