diff --git a/internal/shader/shader.go b/internal/shader/shader.go
index b6783c446..c083932bf 100644
--- a/internal/shader/shader.go
+++ b/internal/shader/shader.go
@@ -315,8 +315,15 @@ func (cs *compileState) parseDecl(b *block, fname string, d ast.Decl) ([]shaderi
 				if !ok {
 					return nil, false
 				}
+				n := s.Name.Name
+				for _, t := range b.types {
+					if t.name == n {
+						cs.addError(s.Pos(), fmt.Sprintf("%s redeclared in this block", n))
+						return nil, false
+					}
+				}
 				b.types = append(b.types, typ{
-					name: s.Name.Name,
+					name: n,
 					ir:   t,
 				})
 			}
diff --git a/internal/shader/syntax_test.go b/internal/shader/syntax_test.go
index a4d01c4e7..a7816f8a6 100644
--- a/internal/shader/syntax_test.go
+++ b/internal/shader/syntax_test.go
@@ -2381,3 +2381,30 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+func TestTypeRedeclaration(t *testing.T) {
+	cases := []struct {
+		stmt string
+		err  bool
+	}{
+		{stmt: "type Foo int; type Foo int", err: true},
+		{stmt: "type Foo int; type Foo float", err: true},
+		{stmt: "type Foo int; type Bar int", err: false},
+	}
+
+	for _, c := range cases {
+		stmt := c.stmt
+		src := fmt.Sprintf(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	%s
+	return position
+}`, stmt)
+		_, err := compileToIR([]byte(src))
+		if err == nil && c.err {
+			t.Errorf("%s must return an error but does not", stmt)
+		} else if err != nil && !c.err {
+			t.Errorf("%s must not return nil but returned %v", stmt, err)
+		}
+	}
+}