diff --git a/.forgejo/workflows/test.yml b/.forgejo/workflows/test.yml
index 59516f3..a549105 100644
--- a/.forgejo/workflows/test.yml
+++ b/.forgejo/workflows/test.yml
@@ -44,5 +44,5 @@ jobs:
       - name: build without docker
         run: go build -tags WITHOUT_DOCKER -v ./...
       - name: test
-        run: go test -v ./pkg/jobparser ./pkg/model
+        run: go test -v ./pkg/jobparser ./pkg/model ./pkg/exprparser
         # TODO test more packages
diff --git a/pkg/exprparser/functions_test.go b/pkg/exprparser/functions_test.go
index ea51a2b..c90b326 100644
--- a/pkg/exprparser/functions_test.go
+++ b/pkg/exprparser/functions_test.go
@@ -43,6 +43,9 @@ func TestFunctionContains(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("contains('one')", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionStartsWith(t *testing.T) {
@@ -72,6 +75,9 @@ func TestFunctionStartsWith(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("startsWith('one')", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionEndsWith(t *testing.T) {
@@ -101,6 +107,9 @@ func TestFunctionEndsWith(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("endsWith('one')", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionJoin(t *testing.T) {
@@ -128,6 +137,9 @@ func TestFunctionJoin(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("join()", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionToJSON(t *testing.T) {
@@ -154,6 +166,9 @@ func TestFunctionToJSON(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("tojson()", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionFromJSON(t *testing.T) {
@@ -177,6 +192,9 @@ func TestFunctionFromJSON(t *testing.T) {
 			assert.Equal(t, tt.expected, output)
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("fromjson()", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
 
 func TestFunctionHashFiles(t *testing.T) {
@@ -248,4 +266,7 @@ func TestFunctionFormat(t *testing.T) {
 			}
 		})
 	}
+
+	_, err := NewInterpeter(env, Config{}).Evaluate("format()", DefaultStatusCheckNone)
+	assert.Error(t, err)
 }
diff --git a/pkg/exprparser/interpreter.go b/pkg/exprparser/interpreter.go
index 29c5686..021e5c9 100644
--- a/pkg/exprparser/interpreter.go
+++ b/pkg/exprparser/interpreter.go
@@ -593,23 +593,58 @@ func (impl *interperterImpl) evaluateFuncCall(funcCallNode *actionlint.FuncCallN
 		args = append(args, reflect.ValueOf(value))
 	}
 
+	argCountCheck := func(argCount int) error {
+		if len(args) != argCount {
+			return fmt.Errorf("'%s' expected %d arguments but got %d instead", funcCallNode.Callee, argCount, len(args))
+		}
+		return nil
+	}
+
+	argAtLeastCheck := func(atLeast int) error {
+		if len(args) < atLeast {
+			return fmt.Errorf("'%s' expected at least %d arguments but got %d instead", funcCallNode.Callee, atLeast, len(args))
+		}
+		return nil
+	}
+
 	switch strings.ToLower(funcCallNode.Callee) {
 	case "contains":
+		if err := argCountCheck(2); err != nil {
+			return nil, err
+		}
 		return impl.contains(args[0], args[1])
 	case "startswith":
+		if err := argCountCheck(2); err != nil {
+			return nil, err
+		}
 		return impl.startsWith(args[0], args[1])
 	case "endswith":
+		if err := argCountCheck(2); err != nil {
+			return nil, err
+		}
 		return impl.endsWith(args[0], args[1])
 	case "format":
+		if err := argAtLeastCheck(1); err != nil {
+			return nil, err
+		}
 		return impl.format(args[0], args[1:]...)
 	case "join":
+		if err := argAtLeastCheck(1); err != nil {
+			return nil, err
+		}
 		if len(args) == 1 {
 			return impl.join(args[0], reflect.ValueOf(","))
 		}
 		return impl.join(args[0], args[1])
 	case "tojson":
+		if err := argCountCheck(1); err != nil {
+			return nil, err
+		}
 		return impl.toJSON(args[0])
 	case "fromjson":
+		if err := argCountCheck(1); err != nil {
+			return nil, err
+		}
 		return impl.fromJSON(args[0])
 	case "hashfiles":
 		if impl.env.HashFiles != nil {