diff --git a/src/analyze.cpp b/src/analyze.cpp
index 0af1baec35b7..983135bbcc02 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -5627,6 +5627,13 @@ ZigType *make_int_type(CodeGen *g, bool is_signed, uint32_t size_in_bits) {
         entry->llvm_type = LLVMIntType(size_in_bits);
         entry->abi_size = LLVMABISizeOfType(g->target_data_ref, entry->llvm_type);
         entry->abi_align = LLVMABIAlignmentOfType(g->target_data_ref, entry->llvm_type);
+        if (size_in_bits >= 128) {
+            // Override the alignment reported by LLVM like Clang does.
+            // On x86_64 there are some instructions like CMPXCHG16B which require this.
+            // See: https://github.com/ziglang/zig/issues/2987
+            assert(entry->abi_align == 8);
+            entry->abi_align = 16;
+        }
     }
 
     const char u_or_i = is_signed ? 'i' : 'u';
@@ -7266,8 +7273,6 @@ static void resolve_llvm_types(CodeGen *g, ZigType *type, ResolveStatus wanted_r
 
 LLVMTypeRef get_llvm_type(CodeGen *g, ZigType *type) {
     assertNoError(type_resolve(g, type, ResolveStatusLLVMFull));
-    assert(type->abi_size == 0 || type->abi_size == LLVMABISizeOfType(g->target_data_ref, type->llvm_type));
-    assert(type->abi_align == 0 || type->abi_align == LLVMABIAlignmentOfType(g->target_data_ref, type->llvm_type));
     return type->llvm_type;
 }
 
diff --git a/test/stage1/behavior/align.zig b/test/stage1/behavior/align.zig
index b64f45bb6b2b..9ea00fb32df2 100644
--- a/test/stage1/behavior/align.zig
+++ b/test/stage1/behavior/align.zig
@@ -167,6 +167,14 @@ test "@ptrCast preserves alignment of bigger source" {
     expect(@typeOf(ptr) == *align(16) u8);
 }
 
+fn give() anyerror!u128 {
+    return 3;
+}
+
+test "return error union with 128-bit integer" {
+    expect(3 == try give());
+}
+
 test "runtime known array index has best alignment possible" {
     // take full advantage of over-alignment
     var array align(4) = [_]u8{ 1, 2, 3, 4 };
@@ -220,6 +228,61 @@ test "alignment of structs" {
     }) == @alignOf(usize));
 }
 
+test "alignment of >= 128-bit integer type" {
+    expect(@alignOf(u128) == 16);
+    expect(@alignOf(u129) == 16);
+}
+
+test "alignment of struct with 128-bit field" {
+    expect(@alignOf(struct {
+        x: u128,
+    }) == 16);
+
+    comptime {
+        expect(@alignOf(struct {
+            x: u128,
+        }) == 16);
+    }
+}
+
+test "size of extern struct with 128-bit field" {
+    expect(@sizeOf(extern struct {
+        x: u128,
+        y: u8,
+    }) == 32);
+
+    comptime {
+        expect(@sizeOf(extern struct {
+            x: u128,
+            y: u8,
+        }) == 32);
+    }
+}
+
+const DefaultAligned = struct {
+    nevermind: u32,
+    badguy: i128,
+};
+
+test "read 128-bit field from default aligned struct in stack memory" {
+    var default_aligned = DefaultAligned {
+        .nevermind = 1,
+        .badguy = 12,
+    };
+    expect((@ptrToInt(&default_aligned.badguy) % 16) == 0);
+    expect(12 == default_aligned.badguy);
+}
+
+var default_aligned_global = DefaultAligned {
+    .nevermind = 1,
+    .badguy = 12,
+};
+
+test "read 128-bit field from default aligned struct in global memory" {
+    expect((@ptrToInt(&default_aligned_global.badguy) % 16) == 0);
+    expect(12 == default_aligned_global.badguy);
+}
+
 test "alignment of extern() void" {
     var runtime_nothing = nothing;
     const casted1 = @ptrCast(*const u8, runtime_nothing);