diff --git a/src/compiler/Compile.go b/src/compiler/Compile.go
index 226c72f..065976b 100644
--- a/src/compiler/Compile.go
+++ b/src/compiler/Compile.go
@@ -37,7 +37,11 @@ func Compile(build *config.Build) (*core.Environment, error) {
 	// We couldn't do that during the scan phase because it's possible
 	// that a field references a type that will only be known after the
 	// full scan is finished.
-	parseFieldTypes(env.Structs(), env)
+	err = parseFieldTypes(env.Structs(), env)
+
+	if err != nil {
+		return nil, err
+	}
 
 	// Parse input and output types so we have type information
 	// ready for all functions before parallel compilation starts.
diff --git a/src/compiler/errors.go b/src/compiler/errors.go
index 9643789..7fef0cb 100644
--- a/src/compiler/errors.go
+++ b/src/compiler/errors.go
@@ -11,6 +11,15 @@ var (
 	MissingMainFunction = errors.String("Missing main function")
 )
 
+// UnknownType error is created when a type could not be found.
+type UnknownType struct {
+	Name string
+}
+
+func (err *UnknownType) Error() string {
+	return fmt.Sprintf("Unknown type '%s'", err.Name)
+}
+
 // UnusedImport error is created when an import is never used.
 type UnusedImport struct {
 	Package string
diff --git a/src/compiler/errors_test.go b/src/compiler/errors_test.go
index 62ee4cd..9a16ca0 100644
--- a/src/compiler/errors_test.go
+++ b/src/compiler/errors_test.go
@@ -15,6 +15,7 @@ var errs = []struct {
 	ExpectedError error
 }{
 	{"MissingMainFunction.q", compiler.MissingMainFunction},
+	{"UnknownType.q", &compiler.UnknownType{Name: "unknown"}},
 	{"UnusedImport.q", &compiler.UnusedImport{Package: "os"}},
 }
 
diff --git a/src/compiler/parseFieldTypes.go b/src/compiler/parseFieldTypes.go
index d08b8a5..80b96e1 100644
--- a/src/compiler/parseFieldTypes.go
+++ b/src/compiler/parseFieldTypes.go
@@ -4,19 +4,27 @@ import (
 	"iter"
 
 	"git.urbach.dev/cli/q/src/core"
+	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/types"
 )
 
 // parseFieldTypes parses the tokens of the struct field types.
-func parseFieldTypes(structs iter.Seq[*types.Struct], env *core.Environment) {
+func parseFieldTypes(structs iter.Seq[*types.Struct], env *core.Environment) error {
 	for structure := range structs {
 		offset := 0
 
 		for i, field := range structure.Fields {
 			field.Type = core.ParseType(field.Tokens[1:], structure.File.Bytes, env)
+
+			if field.Type == nil {
+				return errors.New(&UnknownType{Name: field.Tokens[1:].String(structure.File.Bytes)}, structure.File, field.Tokens[1].Position)
+			}
+
 			field.Index = uint8(i)
 			field.Offset = uint8(offset)
 			offset += field.Type.Size()
 		}
 	}
+
+	return nil
 }
\ No newline at end of file
diff --git a/src/compiler/testdata/UnknownType.q b/src/compiler/testdata/UnknownType.q
new file mode 100644
index 0000000..fc2eef5
--- /dev/null
+++ b/src/compiler/testdata/UnknownType.q
@@ -0,0 +1,6 @@
+Point {
+	x unknown
+	y unknown
+}
+
+main() {}
\ No newline at end of file
diff --git a/src/scanner/scanStruct.go b/src/scanner/scanStruct.go
index f7a8455..5807b6f 100644
--- a/src/scanner/scanStruct.go
+++ b/src/scanner/scanStruct.go
@@ -26,9 +26,8 @@ func (s *scanner) scanStruct(file *fs.File, tokens token.List, i int) (int, erro
 				name := tokens[start].String(file.Bytes)
 
 				structure.AddField(&types.Field{
-					Tokens:   tokens[start:i],
-					Name:     name,
-					Position: token.Position(start),
+					Name:   name,
+					Tokens: tokens[start:i],
 				})
 			}
 
diff --git a/src/types/Field.go b/src/types/Field.go
index aae4cd7..1eced8f 100644
--- a/src/types/Field.go
+++ b/src/types/Field.go
@@ -4,12 +4,11 @@ import "git.urbach.dev/cli/q/src/token"
 
 // Field is a memory region in a data structure.
 type Field struct {
-	Type     Type
-	Name     string
-	Tokens   token.List
-	Position token.Position
-	Index    uint8
-	Offset   uint8
+	Type   Type
+	Name   string
+	Tokens token.List
+	Index  uint8
+	Offset uint8
 }
 
 // String returns the name of the struct.