diff --git a/ssa/builder.go b/ssa/builder.go
index 2686f9cb..69c9869a 100644
--- a/ssa/builder.go
+++ b/ssa/builder.go
@@ -62,10 +62,9 @@ var (
 	tEface      = new(types.Interface)
 
 	// SSA Value constants.
-	vZero  = intConst(0)
-	vOne   = intConst(1)
-	vTrue  = NewConst(exact.MakeBool(true), tBool)
-	vFalse = NewConst(exact.MakeBool(false), tBool)
+	vZero = intConst(0)
+	vOne  = intConst(1)
+	vTrue = NewConst(exact.MakeBool(true), tBool)
 )
 
 // builder holds state associated with the package currently being built.
@@ -314,7 +313,7 @@ func (b *builder) builtin(fn *Function, obj *types.Builtin, args []ast.Expr, typ
 			pos: pos,
 		})
 		fn.currentBlock = fn.newBasicBlock("unreachable")
-		return vFalse // any non-nil Value will do
+		return vTrue // any non-nil Value will do
 	}
 	return nil // treat all others as a regular function call
 }
@@ -1890,7 +1889,8 @@ start:
 		if s.Tok == token.DEC {
 			op = token.SUB
 		}
-		b.assignOp(fn, b.addr(fn, s.X, false), vOne, op)
+		loc := b.addr(fn, s.X, false)
+		b.assignOp(fn, loc, NewConst(exact.MakeInt64(1), loc.typ()), op)
 
 	case *ast.AssignStmt:
 		switch s.Tok {
diff --git a/ssa/const.go b/ssa/const.go
index 5083d997..4b84be8c 100644
--- a/ssa/const.go
+++ b/ssa/const.go
@@ -22,9 +22,10 @@ func NewConst(val exact.Value, typ types.Type) *Const {
 	return &Const{typ, val}
 }
 
-// intConst returns an untyped integer constant that evaluates to i.
+// intConst returns an 'int' constant that evaluates to i.
+// (i is an int64 in case the host is narrower than the target.)
 func intConst(i int64) *Const {
-	return NewConst(exact.MakeInt64(i), types.Typ[types.UntypedInt])
+	return NewConst(exact.MakeInt64(i), types.Typ[types.Int])
 }
 
 // nilConst returns a nil constant of the specified type, which may
diff --git a/ssa/example_test.go b/ssa/example_test.go
index 520f47d9..44c44a3f 100644
--- a/ssa/example_test.go
+++ b/ssa/example_test.go
@@ -101,7 +101,7 @@ func main() {
 	// func main():
 	// .0.entry:                                                               P:0 S:0
 	// 	t0 = new [1]interface{} (varargs)                       *[1]interface{}
-	// 	t1 = &t0[0:untyped integer]                                *interface{}
+	// 	t1 = &t0[0:int]                                            *interface{}
 	// 	t2 = make interface{} <- string ("Hello, World!":string)    interface{}
 	// 	*t1 = t2
 	// 	t3 = slice t0[:]                                          []interface{}
diff --git a/ssa/sanity.go b/ssa/sanity.go
index 9b5bb68a..18bfa8bc 100644
--- a/ssa/sanity.go
+++ b/ssa/sanity.go
@@ -325,6 +325,16 @@ func (s *sanity) checkBlock(b *BasicBlock, index int) {
 			if val == nil {
 				continue // a nil operand is ok
 			}
+
+			// Check that "untyped" types only appear on constant operands.
+			if _, ok := (*op).(*Const); !ok {
+				if basic, ok := (*op).Type().(*types.Basic); ok {
+					if basic.Info()&types.IsUntyped != 0 {
+						s.errorf("operand #%d of %s is untyped: %s", i, instr, basic)
+					}
+				}
+			}
+
 			// Check that Operands that are also Instructions belong to same function.
 			// TODO(adonovan): also check their block dominates block b.
 			if val, ok := val.(Instruction); ok {