diff --git a/src/cmd/compile/internal/types/size.go b/src/cmd/compile/internal/types/size.go
index 7122b2720f..a5a5c0b5b1 100644
--- a/src/cmd/compile/internal/types/size.go
+++ b/src/cmd/compile/internal/types/size.go
@@ -169,7 +169,7 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 	}
 	// Special case: sync/atomic.align64 is an empty struct we recognize
 	// as a signal that the struct it contains must be 64-bit-aligned.
-	if isStruct && t.NumFields() == 0 && t.Sym() != nil && t.Sym().Name == "align64" && isSyncAtomic(t.Sym().Pkg) {
+	if isStruct && t.NumFields() == 0 && t.Sym() != nil && t.Sym().Name == "align64" && isAtomicStdPkg(t.Sym().Pkg) {
 		maxalign = 8
 	}
 	lastzero := int64(0)
@@ -231,8 +231,9 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 	return o
 }
 
-func isSyncAtomic(p *Pkg) bool {
-	return p.Prefix == "sync/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "sync/atomic"
+func isAtomicStdPkg(p *Pkg) bool {
+	return (p.Prefix == "sync/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "sync/atomic") ||
+		(p.Prefix == "runtime/internal/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "runtime/internal/atomic")
 }
 
 // CalcSize calculates and stores the size and alignment for t.
diff --git a/src/runtime/internal/atomic/types.go b/src/runtime/internal/atomic/types.go
index d9cffbf88f..d346a76b67 100644
--- a/src/runtime/internal/atomic/types.go
+++ b/src/runtime/internal/atomic/types.go
@@ -49,9 +49,12 @@ func (i *Int32) Add(delta int32) int32 {
 
 // Int64 is an atomically accessed int64 value.
 //
+// 8-byte aligned on all platforms, unlike a regular int64.
+//
 // An Int64 must not be copied.
 type Int64 struct {
 	noCopy noCopy
+	_      align64
 	value  int64
 }
 
@@ -242,9 +245,12 @@ func (u *Uint32) Add(delta int32) uint32 {
 
 // Uint64 is an atomically accessed uint64 value.
 //
+// 8-byte aligned on all platforms, unlike a regular uint64.
+//
 // A Uint64 must not be copied.
 type Uint64 struct {
 	noCopy noCopy
+	_      align64
 	value  uint64
 }
 
@@ -346,9 +352,11 @@ func (u *Uintptr) Add(delta uintptr) uintptr {
 
 // Float64 is an atomically accessed float64 value.
 //
+// 8-byte aligned on all platforms, unlike a regular float64.
+//
 // A Float64 must not be copied.
 type Float64 struct {
-	// Inherits noCopy from Uint64.
+	// Inherits noCopy and align64 from Uint64.
 	u Uint64
 }
 
@@ -416,3 +424,8 @@ type noCopy struct{}
 // Lock is a no-op used by -copylocks checker from `go vet`.
 func (*noCopy) Lock()   {}
 func (*noCopy) Unlock() {}
+
+// align64 may be added to structs that must be 64-bit aligned.
+// This struct is recognized by a special case in the compiler
+// and will not work if copied to any other package.
+type align64 struct{}