diff --git a/internal/shaderir/glsl/glsl.go b/internal/shaderir/glsl/glsl.go
index 85fa1e9d9..8a0d2eb87 100644
--- a/internal/shaderir/glsl/glsl.go
+++ b/internal/shaderir/glsl/glsl.go
@@ -504,9 +504,9 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 			var op string
 			switch e.Op {
 			case shaderir.Add, shaderir.Sub, shaderir.NotOp:
-				op = string(e.Op)
+				op = opString(e.Op)
 			default:
-				op = fmt.Sprintf("?(unexpected op: %s)", string(e.Op))
+				op = fmt.Sprintf("?(unexpected op: %d)", e.Op)
 			}
 			return fmt.Sprintf("%s(%s)", op, expr(&e.Exprs[0]))
 		case shaderir.Binary:
@@ -514,7 +514,7 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 				// '%' is not defined.
 				return fmt.Sprintf("modInt((%s), (%s))", expr(&e.Exprs[0]), expr(&e.Exprs[1]))
 			}
-			return fmt.Sprintf("(%s) %s (%s)", expr(&e.Exprs[0]), e.Op, expr(&e.Exprs[1]))
+			return fmt.Sprintf("(%s) %s (%s)", expr(&e.Exprs[0]), opString(e.Op), expr(&e.Exprs[1]))
 		case shaderir.Selection:
 			return fmt.Sprintf("(%s) ? (%s) : (%s)", expr(&e.Exprs[0]), expr(&e.Exprs[1]), expr(&e.Exprs[2]))
 		case shaderir.Call:
@@ -594,9 +594,9 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 			var op string
 			switch s.ForOp {
 			case shaderir.LessThanOp, shaderir.LessThanEqualOp, shaderir.GreaterThanOp, shaderir.GreaterThanEqualOp, shaderir.EqualOp, shaderir.NotEqualOp:
-				op = string(s.ForOp)
+				op = opString(s.ForOp)
 			default:
-				op = fmt.Sprintf("?(unexpected op: %s)", string(s.ForOp))
+				op = fmt.Sprintf("?(unexpected op: %d)", s.ForOp)
 			}
 
 			t := s.ForVarType
diff --git a/internal/shaderir/glsl/type.go b/internal/shaderir/glsl/type.go
index f8e35f540..bd1f71c4e 100644
--- a/internal/shaderir/glsl/type.go
+++ b/internal/shaderir/glsl/type.go
@@ -20,6 +20,50 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
 )
 
+func opString(op shaderir.Op) string {
+	switch op {
+	case shaderir.Add:
+		return "+"
+	case shaderir.Sub:
+		return "-"
+	case shaderir.NotOp:
+		return "!"
+	case shaderir.Mul:
+		return "*"
+	case shaderir.Div:
+		return "/"
+	case shaderir.ModOp:
+		return "%"
+	case shaderir.LeftShift:
+		return "<<"
+	case shaderir.RightShift:
+		return ">>"
+	case shaderir.LessThanOp:
+		return "<"
+	case shaderir.LessThanEqualOp:
+		return "<="
+	case shaderir.GreaterThanOp:
+		return ">"
+	case shaderir.GreaterThanEqualOp:
+		return ">="
+	case shaderir.EqualOp:
+		return "=="
+	case shaderir.NotEqualOp:
+		return "!="
+	case shaderir.And:
+		return "&"
+	case shaderir.Xor:
+		return "^"
+	case shaderir.Or:
+		return "|"
+	case shaderir.AndAnd:
+		return "&&"
+	case shaderir.OrOr:
+		return "||"
+	}
+	return fmt.Sprintf("!(unexpected operator: %d)", op)
+}
+
 func typeString(t *shaderir.Type) (string, string) {
 	switch t.Main {
 	case shaderir.Array:
diff --git a/internal/shaderir/msl/msl.go b/internal/shaderir/msl/msl.go
index 0ecf0c92f..b763cbe8f 100644
--- a/internal/shaderir/msl/msl.go
+++ b/internal/shaderir/msl/msl.go
@@ -371,13 +371,13 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 			var op string
 			switch e.Op {
 			case shaderir.Add, shaderir.Sub, shaderir.NotOp:
-				op = string(e.Op)
+				op = opString(e.Op)
 			default:
-				op = fmt.Sprintf("?(unexpected op: %s)", string(e.Op))
+				op = fmt.Sprintf("?(unexpected op: %d)", e.Op)
 			}
 			return fmt.Sprintf("%s(%s)", op, expr(&e.Exprs[0]))
 		case shaderir.Binary:
-			return fmt.Sprintf("(%s) %s (%s)", expr(&e.Exprs[0]), e.Op, expr(&e.Exprs[1]))
+			return fmt.Sprintf("(%s) %s (%s)", expr(&e.Exprs[0]), opString(e.Op), expr(&e.Exprs[1]))
 		case shaderir.Selection:
 			return fmt.Sprintf("(%s) ? (%s) : (%s)", expr(&e.Exprs[0]), expr(&e.Exprs[1]), expr(&e.Exprs[2]))
 		case shaderir.Call:
@@ -469,9 +469,9 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 			var op string
 			switch s.ForOp {
 			case shaderir.LessThanOp, shaderir.LessThanEqualOp, shaderir.GreaterThanOp, shaderir.GreaterThanEqualOp, shaderir.EqualOp, shaderir.NotEqualOp:
-				op = string(s.ForOp)
+				op = opString(s.ForOp)
 			default:
-				op = fmt.Sprintf("?(unexpected op: %s)", string(s.ForOp))
+				op = fmt.Sprintf("?(unexpected op: %d)", s.ForOp)
 			}
 
 			t := s.ForVarType
diff --git a/internal/shaderir/msl/type.go b/internal/shaderir/msl/type.go
index 9bcae79aa..6484cc31d 100644
--- a/internal/shaderir/msl/type.go
+++ b/internal/shaderir/msl/type.go
@@ -20,6 +20,50 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
 )
 
+func opString(op shaderir.Op) string {
+	switch op {
+	case shaderir.Add:
+		return "+"
+	case shaderir.Sub:
+		return "-"
+	case shaderir.NotOp:
+		return "!"
+	case shaderir.Mul:
+		return "*"
+	case shaderir.Div:
+		return "/"
+	case shaderir.ModOp:
+		return "%"
+	case shaderir.LeftShift:
+		return "<<"
+	case shaderir.RightShift:
+		return ">>"
+	case shaderir.LessThanOp:
+		return "<"
+	case shaderir.LessThanEqualOp:
+		return "<="
+	case shaderir.GreaterThanOp:
+		return ">"
+	case shaderir.GreaterThanEqualOp:
+		return ">="
+	case shaderir.EqualOp:
+		return "=="
+	case shaderir.NotEqualOp:
+		return "!="
+	case shaderir.And:
+		return "&"
+	case shaderir.Xor:
+		return "^"
+	case shaderir.Or:
+		return "|"
+	case shaderir.AndAnd:
+		return "&&"
+	case shaderir.OrOr:
+		return "||"
+	}
+	return fmt.Sprintf("!(unexpected operator: %d)", op)
+}
+
 func typeString(t *shaderir.Type, packed bool, ref bool) string {
 	switch t.Main {
 	case shaderir.Array:
diff --git a/internal/shaderir/program.go b/internal/shaderir/program.go
index 21ad87d67..2ae6d59f3 100644
--- a/internal/shaderir/program.go
+++ b/internal/shaderir/program.go
@@ -131,28 +131,28 @@ const (
 	Index
 )
 
-type Op string
+type Op int
 
 const (
-	Add                Op = "+"
-	Sub                Op = "-"
-	NotOp              Op = "!"
-	Mul                Op = "*"
-	Div                Op = "/"
-	ModOp              Op = "%"
-	LeftShift          Op = "<<"
-	RightShift         Op = ">>"
-	LessThanOp         Op = "<"
-	LessThanEqualOp    Op = "<="
-	GreaterThanOp      Op = ">"
-	GreaterThanEqualOp Op = ">="
-	EqualOp            Op = "=="
-	NotEqualOp         Op = "!="
-	And                Op = "&"
-	Xor                Op = "^"
-	Or                 Op = "|"
-	AndAnd             Op = "&&"
-	OrOr               Op = "||"
+	Add Op = iota
+	Sub
+	NotOp
+	Mul // TODO: Separate Hadamard-product and Matrix-product
+	Div
+	ModOp
+	LeftShift
+	RightShift
+	LessThanOp
+	LessThanEqualOp
+	GreaterThanOp
+	GreaterThanEqualOp
+	EqualOp
+	NotEqualOp
+	And
+	Xor
+	Or
+	AndAnd
+	OrOr
 )
 
 func OpFromToken(t token.Token) (Op, bool) {
@@ -196,7 +196,7 @@ func OpFromToken(t token.Token) (Op, bool) {
 	case token.LOR:
 		return OrOr, true
 	}
-	return "", false
+	return 0, false
 }
 
 type BuiltinFunc string