diff --git a/internal/shader/stmt.go b/internal/shader/stmt.go
index 2ac5e7bdb..943dfb36e 100644
--- a/internal/shader/stmt.go
+++ b/internal/shader/stmt.go
@@ -346,7 +346,7 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 		})
 
 	case *ast.IncDecStmt:
-		exprs, _, ss, ok := cs.parseExpr(block, stmt.X, false)
+		exprs, _, ss, ok := cs.parseExpr(block, stmt.X, true)
 		if !ok {
 			return nil, false
 		}
diff --git a/shader_test.go b/shader_test.go
index c322db999..d58d43254 100644
--- a/shader_test.go
+++ b/shader_test.go
@@ -225,7 +225,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	return vec4(0)
 }
 `)); err != nil {
-		t.Errorf("error must be nil but non-nil: %v", err)
+		t.Error(err)
 	}
 
 	if _, err := NewShader([]byte(`package main
@@ -236,7 +236,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	return vec4(0)
 }
 `)); err != nil {
-		t.Errorf("error must be nil but non-nil: %v", err)
+		t.Error(err)
 	}
 }
 
@@ -576,6 +576,8 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		t.Errorf("error must be non-nil but was nil")
 	}
 
+	// Increment statement treats a variable 'used'.
+	// https://play.golang.org/p/2RuYMrSLjt3
 	if _, err := NewShader([]byte(`package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
@@ -583,8 +585,8 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	x++
 	return vec4(0)
 }
-`)); err == nil {
-		t.Errorf("error must be non-nil but was nil")
+`)); err != nil {
+		t.Error(err)
 	}
 }
 
@@ -630,6 +632,16 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	_ = x
 	return vec4(0)
 }
+`)); err == nil {
+		t.Errorf("error must be non-nil but was nil")
+	}
+
+	if _, err := NewShader([]byte(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	_++
+	return vec4(0)
+}
 `)); err == nil {
 		t.Errorf("error must be non-nil but was nil")
 	}