diff --git a/src/librustc/middle/trans/adt.rs b/src/librustc/middle/trans/adt.rs
index da78b650852..d26c423b74a 100644
--- a/src/librustc/middle/trans/adt.rs
+++ b/src/librustc/middle/trans/adt.rs
@@ -766,6 +766,26 @@ pub fn trans_const(ccx: &CrateContext, r: &Repr, discr: Disr,
     }
 }
 
+/**
+ * Compute struct field offsets relative to struct begin.
+ */
+fn compute_struct_field_offsets(ccx: &CrateContext, st: &Struct) -> Vec<u64> {
+    let mut offsets = vec!();
+
+    let mut offset = 0;
+    for &ty in st.fields.iter() {
+        let llty = type_of::sizing_type_of(ccx, ty);
+        if !st.packed {
+            let type_align = machine::llalign_of_min(ccx, llty) as u64;
+            offset = roundup(offset, type_align);
+        }
+        offsets.push(offset);
+        offset += machine::llsize_of_alloc(ccx, llty) as u64;
+    }
+    assert_eq!(st.fields.len(), offsets.len());
+    offsets
+}
+
 /**
  * Building structs is a little complicated, because we might need to
  * insert padding if a field's value is less aligned than its type.
@@ -780,26 +800,32 @@ fn build_const_struct(ccx: &CrateContext, st: &Struct, vals: &[ValueRef])
     -> Vec<ValueRef> {
     assert_eq!(vals.len(), st.fields.len());
 
+    let target_offsets = compute_struct_field_offsets(ccx, st);
+
+    // offset of current value
     let mut offset = 0;
     let mut cfields = Vec::new();
-    for (i, &ty) in st.fields.iter().enumerate() {
-        let llty = type_of::sizing_type_of(ccx, ty);
-        let type_align = machine::llalign_of_min(ccx, llty)
-            /*bad*/as u64;
-        let val_align = machine::llalign_of_min(ccx, val_ty(vals[i]))
-            /*bad*/as u64;
-        let target_offset = roundup(offset, type_align);
-        offset = roundup(offset, val_align);
+    for (&val, &target_offset) in vals.iter().zip(target_offsets.iter()) {
+        if !st.packed {
+            let val_align = machine::llalign_of_min(ccx, val_ty(val))
+                /*bad*/as u64;
+            offset = roundup(offset, val_align);
+        }
         if offset != target_offset {
             cfields.push(padding(ccx, target_offset - offset));
             offset = target_offset;
         }
-        assert!(!is_undef(vals[i]));
-        cfields.push(vals[i]);
-        offset += machine::llsize_of_alloc(ccx, llty) as u64
+        assert!(!is_undef(val));
+        cfields.push(val);
+        offset += machine::llsize_of_alloc(ccx, val_ty(val)) as u64;
     }
 
-    return cfields;
+    assert!(offset <= st.size);
+    if offset != st.size {
+        cfields.push(padding(ccx, st.size - offset));
+    }
+
+    cfields
 }
 
 fn padding(ccx: &CrateContext, size: u64) -> ValueRef {
diff --git a/src/test/run-pass/trans-tag-static-padding.rs b/src/test/run-pass/trans-tag-static-padding.rs
new file mode 100644
index 00000000000..c6a3a0b0409
--- /dev/null
+++ b/src/test/run-pass/trans-tag-static-padding.rs
@@ -0,0 +1,66 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+// Issue #13186
+
+// For simplicity of explanations assuming code is compiled for x86_64
+// Linux ABI.
+
+// Size of TestOption<u64> is 16, and alignment of TestOption<u64> is 8.
+// Size of u8 is 1, and alignment of u8 is 1.
+// So size of Request is 24, and alignment of Request must be 8:
+// the maximum alignment of its fields.
+// Last 7 bytes of Request struct are not occupied by any fields.
+
+
+enum TestOption<T> {
+    TestNone,
+    TestSome(T),
+}
+
+pub struct Request {
+    foo: TestOption<u64>,
+    bar: u8,
+}
+
+fn default_instance() -> &'static Request {
+    static instance: Request = Request {
+        // LLVM does not allow to specify alignment of expressions, thus
+        // alignment of `foo` in constant is 1, not 8.
+        foo: TestNone,
+        bar: 17,
+        // Space after last field is not occupied by any data, but it is
+        // reserved to make struct aligned properly. If compiler does
+        // not insert padding after last field when emitting constant,
+        // size of struct may be not equal to size of struct, and
+        // compiler crashes in internal assertion check.
+    };
+    &'static instance
+}
+
+fn non_default_instance() -> &'static Request {
+    static instance: Request = Request {
+        foo: TestSome(0x1020304050607080),
+        bar: 19,
+    };
+    &'static instance
+}
+
+pub fn main() {
+    match default_instance() {
+        &Request { foo: TestNone, bar: 17 } => {},
+        _ => fail!(),
+    };
+    match non_default_instance() {
+        &Request { foo: TestSome(0x1020304050607080), bar: 19 } => {},
+        _ => fail!(),
+    };
+}