diff --git a/compiler/compiler.go b/compiler/compiler.go
index d8e76e6a7..141522603 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -60,7 +60,7 @@ func (l *compiler) NewDeleteQuery(rctx *runtime.Context, ast *parser.AST, head *
 	if err = optimizer.New(rctx, l.env).OptimizeDeleter(main, Parallelism); err != nil {
 		return nil, err
 	}
-	outputs, debugs, b, err := BuildWithBuilder(rctx, main, l.env, nil)
+	outputs, debugs, b, err := BuildWithBuilder(rctx, main, l.env)
 	if err != nil {
 		return nil, err
 	}
diff --git a/compiler/package.go b/compiler/package.go
index db877cb10..9f15ab87f 100644
--- a/compiler/package.go
+++ b/compiler/package.go
@@ -43,18 +43,18 @@ func Optimize(ctx context.Context, main *dag.Main, env *exec.Environment, parall
 	return nil
 }
 
-func Build(rctx *runtime.Context, main *dag.Main, env *exec.Environment, readers []sio.Reader) (map[string]vio.Puller, *op.DebugChans, vio.Meter, error) {
+func Build(rctx *runtime.Context, main *dag.Main, env *exec.Environment) (map[string]vio.Puller, *op.DebugChans, vio.Meter, error) {
 	b := rungen.NewBuilder(rctx, env)
-	outputs, debugs, err := b.Build(main, readers...)
+	outputs, debugs, err := b.Build(main)
 	if err != nil {
 		return nil, nil, nil, err
 	}
 	return outputs, debugs, b.Meter(), nil
 }
 
-func BuildWithBuilder(rctx *runtime.Context, main *dag.Main, env *exec.Environment, readers []sio.Reader) (map[string]vio.Puller, *op.DebugChans, *rungen.Builder, error) {
+func BuildWithBuilder(rctx *runtime.Context, main *dag.Main, env *exec.Environment) (map[string]vio.Puller, *op.DebugChans, *rungen.Builder, error) {
 	b := rungen.NewBuilder(rctx, env)
-	outputs, debugs, err := b.Build(main, readers...)
+	outputs, debugs, err := b.Build(main)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -76,7 +76,7 @@ func CompileWithAST(rctx *runtime.Context, ast *parser.AST, env *exec.Environmen
 			return nil, err
 		}
 	}
-	outputs, debugs, meter, err := Build(rctx, main, env, nil)
+	outputs, debugs, meter, err := Build(rctx, main, env)
 	if err != nil {
 		return nil, err
 	}
diff --git a/compiler/rungen/op.go b/compiler/rungen/op.go
index f9defb5ef..8dc4c245c 100644
--- a/compiler/rungen/op.go
+++ b/compiler/rungen/op.go
@@ -42,7 +42,6 @@ import (
 	vamexpr "github.com/brimdata/super/runtime/vam/expr"
 	vamop "github.com/brimdata/super/runtime/vam/op"
 	"github.com/brimdata/super/sbuf"
-	"github.com/brimdata/super/sio"
 	"github.com/brimdata/super/vector/vio"
 	"github.com/segmentio/ksuid"
 )
@@ -54,7 +53,6 @@ type Builder struct {
 	mctx            *super.Context
 	mapper          *super.TypeDefsMapper
 	env             *exec.Environment
-	readers         []sio.Reader
 	progress        *vio.Progress
 	debugs          *vamop.DebugChans
 	channels        map[string][]vio.Puller
@@ -83,13 +81,11 @@ func NewBuilder(rctx *runtime.Context, env *exec.Environment) *Builder {
 	}
 }
 
-// Build builds a flowgraph for main.  If main contains a dag.DefaultSource, it
-// will read from readers.
-func (b *Builder) Build(main *dag.Main, readers ...sio.Reader) (map[string]vio.Puller, *vamop.DebugChans, error) {
+// Build builds a flowgraph for main.
+func (b *Builder) Build(main *dag.Main) (map[string]vio.Puller, *vamop.DebugChans, error) {
 	if !isEntry(main.Body) {
 		return nil, nil, errors.New("internal error: DAG entry point is not a data source")
 	}
-	b.readers = readers
 	if len(main.Types) != 0 {
 		defs, ok := super.NewTypeDefsFromBytes(main.Types)
 		if !ok {
diff --git a/runtime/sam/expr/filter_test.go b/runtime/sam/expr/filter_test.go
index 255c4e0dc..773d2e808 100644
--- a/runtime/sam/expr/filter_test.go
+++ b/runtime/sam/expr/filter_test.go
@@ -63,7 +63,7 @@ func runCasesHelper(t *testing.T, record string, cases []testcase, expectBufferF
 			require.NoError(t, err, "filter: %q", c.filter)
 			err = compiler.Optimize(rctx, main, env, 0)
 			require.NoError(t, err, "filter: %q", c.filter)
-			_, _, builder, err := compiler.BuildWithBuilder(rctx, main, env, nil)
+			_, _, builder, err := compiler.BuildWithBuilder(rctx, main, env)
 			require.NoError(t, err, "filter: %q", c.filter)
 			scan, ok := main.Body[0].(*dag.FileScan)
 			require.True(t, ok)