diff --git a/internal/interpreter/interpreter.go b/internal/interpreter/interpreter.go
index d9a6730..b04a581 100644
--- a/internal/interpreter/interpreter.go
+++ b/internal/interpreter/interpreter.go
@@ -177,6 +177,10 @@ func (s *programState) parseVars(varDeclrs []parser.VarDeclaration, rawVars map[
 	return nil
 }
 
+type FeatureFlag = string
+
+const ExperimentalOverdraftFunctionFeatureFlag FeatureFlag = "experimental-overdraft-function"
+
 func RunProgram(
 	ctx context.Context,
 	program parser.Program,
@@ -196,6 +200,10 @@ func RunProgram(
 		ctx:                 ctx,
 	}
 
+	if _, ok := featureFlags[ExperimentalOverdraftFunctionFeatureFlag]; ok {
+		st.OverdraftFunctionFeatureFlag = true
+	}
+
 	err := st.parseVars(program.Vars, vars)
 	if err != nil {
 		return nil, err
@@ -252,6 +260,8 @@ type programState struct {
 	CachedBalances     Balances
 
 	CurrentBalanceQuery BalanceQuery
+
+	OverdraftFunctionFeatureFlag bool
 }
 
 func (st *programState) runStatement(statement parser.Statement) ([]Posting, InterpreterError) {
diff --git a/internal/interpreter/interpreter_error.go b/internal/interpreter/interpreter_error.go
index 168df11..c819f1a 100644
--- a/internal/interpreter/interpreter_error.go
+++ b/internal/interpreter/interpreter_error.go
@@ -184,3 +184,12 @@ type QueryMetadataError struct {
 func (e QueryMetadataError) Error() string {
 	return e.WrappedError.Error()
 }
+
+type ExperimentalFeature struct {
+	parser.Range
+	FlagName string
+}
+
+func (e ExperimentalFeature) Error() string {
+	return fmt.Sprintf("this feature is experimental. You need the '%s' feature flag to enable it", e.FlagName)
+}
diff --git a/internal/interpreter/interpreter_test.go b/internal/interpreter/interpreter_test.go
index 14762db..4508e0c 100644
--- a/internal/interpreter/interpreter_test.go
+++ b/internal/interpreter/interpreter_test.go
@@ -82,16 +82,50 @@ func (c *TestCase) setBalance(account string, asset string, amount int64) {
 }
 
 func test(t *testing.T, testCase TestCase) {
+	testWithFeatureFlag(t, testCase, "")
+}
+
+// A version of test() which tests code under a feature flag
+// if the feature flag is the empty string, it behaves as test()
+// otherwise, it tests the program under that feature flag and also tests that
+// the same script, without the flag, yields the ExperimentalFeature{} error
+func testWithFeatureFlag(t *testing.T, testCase TestCase, flagName string) {
 	t.Parallel()
 
 	prog := testCase.program
 
 	require.NotNil(t, prog)
 
-	execResult, err := machine.RunProgram(context.Background(), *prog, testCase.vars, machine.StaticStore{
-		testCase.balances,
-		testCase.meta,
-	}, nil)
+	featureFlags := map[string]struct{}{}
+	if flagName != "" {
+		featureFlags[flagName] = struct{}{}
+
+		_, err := machine.RunProgram(
+			context.Background(),
+			*prog,
+			testCase.vars,
+			machine.StaticStore{
+				testCase.balances,
+				testCase.meta,
+			},
+			nil,
+		)
+
+		require.Equal(t, machine.ExperimentalFeature{
+			FlagName: flagName,
+		}, removeRange(err))
+	}
+
+	execResult, err := machine.RunProgram(
+		context.Background(),
+		*prog,
+		testCase.vars,
+		machine.StaticStore{
+			testCase.balances,
+			testCase.meta,
+		},
+		featureFlags,
+	)
 
 	expected := testCase.expected
 	if expected.Error != nil {
@@ -3207,7 +3241,6 @@ func TestSaveFromAccount(t *testing.T) {
 	})
 }
 
-// new semantics
 func TestOverdraftFunctionWhenNegative(t *testing.T) {
 	script := `
  		vars { monetary $amt = overdraft(@acc, EUR/2) }
@@ -3234,7 +3267,7 @@ func TestOverdraftFunctionWhenNegative(t *testing.T) {
 		},
 		Error: nil,
 	}
-	test(t, tc)
+	testWithFeatureFlag(t, tc, machine.ExperimentalOverdraftFunctionFeatureFlag)
 }
 
 func TestOverdraftFunctionWhenZero(t *testing.T) {
@@ -3257,7 +3290,7 @@ func TestOverdraftFunctionWhenZero(t *testing.T) {
 		},
 		Error: nil,
 	}
-	test(t, tc)
+	testWithFeatureFlag(t, tc, machine.ExperimentalOverdraftFunctionFeatureFlag)
 }
 
 func TestOverdraftFunctionWhenPositive(t *testing.T) {
@@ -3281,7 +3314,7 @@ func TestOverdraftFunctionWhenPositive(t *testing.T) {
 		},
 		Error: nil,
 	}
-	test(t, tc)
+	testWithFeatureFlag(t, tc, machine.ExperimentalOverdraftFunctionFeatureFlag)
 }
 
 func TestOverdraftFunctionUseCaseRemoveDebt(t *testing.T) {
@@ -3316,5 +3349,5 @@ func TestOverdraftFunctionUseCaseRemoveDebt(t *testing.T) {
 		},
 		Error: nil,
 	}
-	test(t, tc)
+	testWithFeatureFlag(t, tc, machine.ExperimentalOverdraftFunctionFeatureFlag)
 }