diff --git a/internal/shader/expr.go b/internal/shader/expr.go
index 5dc9a32dc..6373e251d 100644
--- a/internal/shader/expr.go
+++ b/internal/shader/expr.go
@@ -286,6 +286,14 @@ func (cs *compileState) parseExpr(block *block, expr ast.Expr) ([]shaderir.Expr,
 
 		f := cs.funcs[callee.Index]
 
+		for i, p := range f.ir.InParams {
+			if args[i].Type == shaderir.NumberExpr && p.Main == shaderir.Int {
+				if !cs.forceToInt(e, &args[i]) {
+					return nil, nil, nil, false
+				}
+			}
+		}
+
 		var outParams []int
 		for _, p := range f.ir.OutParams {
 			idx := block.totalLocalVariableNum()
diff --git a/internal/shader/shader_test.go b/internal/shader/shader_test.go
index c09c0b088..aaf4af4fb 100644
--- a/internal/shader/shader_test.go
+++ b/internal/shader/shader_test.go
@@ -15,6 +15,7 @@
 package shader_test
 
 import (
+	"fmt"
 	"go/parser"
 	"go/token"
 	"io/ioutil"
@@ -117,7 +118,24 @@ func TestCompile(t *testing.T) {
 			}
 			vs, fs := glsl.Compile(s)
 			if got, want := normalize(vs), normalize(string(tc.VS)); got != want {
-				t.Errorf("got: %v, want: %v", got, want)
+				var msg string
+				gotlines := strings.Split(got, "\n")
+				wantlines := strings.Split(want, "\n")
+				for i := range gotlines {
+					if len(wantlines) <= i {
+						msg = fmt.Sprintf(`lines %d:
+got:  %s
+want: (out of range)`, i+1, gotlines[i])
+						break
+					}
+					if gotlines[i] != wantlines[i] {
+						msg = fmt.Sprintf(`lines %d:
+got:  %s
+want: %s`, i+1, gotlines[i], wantlines[i])
+						break
+					}
+				}
+				t.Errorf("got: %v, want: %v\n\n%s", got, want, msg)
 			}
 			if tc.FS != nil {
 				if got, want := normalize(fs), normalize(string(tc.FS)); got != want {
diff --git a/internal/shader/stmt.go b/internal/shader/stmt.go
index d1f718300..12424c962 100644
--- a/internal/shader/stmt.go
+++ b/internal/shader/stmt.go
@@ -24,9 +24,9 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/shaderir"
 )
 
-func (cs *compileState) forceToInt(stmt ast.Stmt, expr *shaderir.Expr) bool {
+func (cs *compileState) forceToInt(node ast.Node, expr *shaderir.Expr) bool {
 	if !canTruncateToInteger(expr.Const) {
-		cs.addError(stmt.Pos(), fmt.Sprintf("constant %s truncated to integer", expr.Const.String()))
+		cs.addError(node.Pos(), fmt.Sprintf("constant %s truncated to integer", expr.Const.String()))
 		return false
 	}
 	expr.ConstType = shaderir.ConstTypeInt
diff --git a/internal/shader/testdata/number.expected.vs b/internal/shader/testdata/number.expected.vs
index 00a5577c1..4c02e6d0e 100644
--- a/internal/shader/testdata/number.expected.vs
+++ b/internal/shader/testdata/number.expected.vs
@@ -2,6 +2,9 @@ void F0(out vec2 l0);
 void F1(out vec2 l0);
 void F2(out float l0);
 void F3(out int l0);
+void F4(in float l0);
+void F5(in int l0);
+void F6(void);
 
 void F0(out vec2 l0) {
 	float l1 = float(0);
@@ -46,3 +49,14 @@ void F3(out int l0) {
 	l0 = 1;
 	return;
 }
+
+void F4(in float l0) {
+}
+
+void F5(in int l0) {
+}
+
+void F6(void) {
+	F4(1.0);
+	F5(1);
+}
diff --git a/internal/shader/testdata/number.go b/internal/shader/testdata/number.go
index c99279cd2..38894e0e9 100644
--- a/internal/shader/testdata/number.go
+++ b/internal/shader/testdata/number.go
@@ -17,5 +17,16 @@ func Float() float {
 }
 
 func Int() int {
-	return 1
+	return 1.0
+}
+
+func TakeFloat(x float) {
+}
+
+func TakeInt(x int) {
+}
+
+func Foo3() {
+	TakeFloat(1.0)
+	TakeInt(1.0)
 }