diff --git a/src/common/error.go b/src/common/error.go
new file mode 100644
index 0000000000..1e16ce4dcf
--- /dev/null
+++ b/src/common/error.go
@@ -0,0 +1,19 @@
+package common
+
+const (
+	WrongNumberOfArguments = iota
+	InvalidArgument
+)
+
+type QueryError struct {
+	ErrorCode int
+	ErrorMsg  string
+}
+
+func (self *QueryError) Error() string {
+	return self.ErrorMsg
+}
+
+func NewQueryError(code int, msg string) *QueryError {
+	return &QueryError{code, msg}
+}
diff --git a/src/engine/engine.go b/src/engine/engine.go
index 3bd69f48ed..06aea7089e 100644
--- a/src/engine/engine.go
+++ b/src/engine/engine.go
@@ -105,7 +105,8 @@ type Mapper func(*protocol.Point) interface{}
 type InverseMapper func(interface{}, int) interface{}
 
 func createValuesToInterface(groupBy parser.GroupByClause, definitions []*protocol.FieldDefinition) (Mapper, InverseMapper) {
-	window, ok := groupBy.GetGroupByTime()
+	// we shouldn't get an error, this is checked earlier in the executeCountQueryWithGroupBy
+	window, _ := groupBy.GetGroupByTime()
 	names := []string{}
 	for _, value := range groupBy {
 		names = append(names, value.Name)
@@ -125,8 +126,8 @@ func createValuesToInterface(groupBy parser.GroupByClause, definitions []*protoc
 		}
 
 		return func(p *protocol.Point) interface{} {
-				if ok {
-					return getTimestampFromPoint(window, p)
+				if window != nil {
+					return getTimestampFromPoint(*window, p)
 				} else {
 					return getValueFromPoint(p.Values[idx], fType)
 				}
@@ -175,7 +176,10 @@ func (self *QueryEngine) executeCountQueryWithGroupBy(query *parser.Query, yield
 	fieldTypes := map[string]*protocol.FieldDefinition_Type{}
 	var inverse InverseMapper
 
-	duration, ok := groupBy.GetGroupByTime()
+	duration, err := groupBy.GetGroupByTime()
+	if err != nil {
+		return err
+	}
 
 	self.coordinator.DistributeQuery(query, func(series *protocol.Series) error {
 		var mapper Mapper
@@ -190,8 +194,8 @@ func (self *QueryEngine) executeCountQueryWithGroupBy(query *parser.Query, yield
 			c := counts[value]
 			counts[value] = c + 1
 
-			if ok {
-				timestamps[value] = getTimestampFromPoint(duration, point)
+			if duration != nil {
+				timestamps[value] = getTimestampFromPoint(*duration, point)
 			} else {
 				timestamps[value] = point.GetTimestamp()
 			}
diff --git a/src/engine/engine_test.go b/src/engine/engine_test.go
index b8bae0f8c1..34941d5658 100644
--- a/src/engine/engine_test.go
+++ b/src/engine/engine_test.go
@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"common"
 	"encoding/json"
 	"fmt"
 	. "launchpad.net/gocheck"
@@ -58,6 +59,15 @@ func createEngine(c *C, seriesString string) EngineI {
 //
 // expectedSeries must be a json array, e.g. time series must by
 // inclosed in '[' and ']'
+func runQueryRunError(engine EngineI, query string, c *C, expectedErr error) {
+	q, err := parser.ParseQuery(query)
+	c.Assert(err, IsNil)
+
+	err = engine.RunQuery(q, func(series *protocol.Series) error { return nil })
+
+	c.Assert(err, DeepEquals, expectedErr)
+}
+
 func runQuery(engine EngineI, query string, c *C, expectedSeries string) {
 	q, err := parser.ParseQuery(query)
 	c.Assert(err, IsNil)
@@ -508,6 +518,7 @@ func (self *EngineSuite) TestCountQueryWithGroupByClauseWithMultipleColumns(c *C
 `)
 
 }
+
 func (self *EngineSuite) TestCountQueryWithGroupByTime(c *C) {
 	// make the mock coordinator return some data
 	engine := createEngine(c, `
@@ -587,3 +598,15 @@ func (self *EngineSuite) TestCountQueryWithGroupByTime(c *C) {
 `)
 
 }
+
+func (self *EngineSuite) TestCountQueryWithGroupByTimeInvalidNumberOfArguments(c *C) {
+	err := common.NewQueryError(common.WrongNumberOfArguments, "time function only accepts one argument")
+	engine := createEngine(c, `[]`)
+	runQueryRunError(engine, "select count(*) from foo group by time(1h, 1m);", c, err)
+}
+
+func (self *EngineSuite) TestCountQueryWithGroupByTimeInvalidArgument(c *C) {
+	err := common.NewQueryError(common.InvalidArgument, "invalid argument foobar to the time function")
+	engine := createEngine(c, `[]`)
+	runQueryRunError(engine, "select count(*) from foo group by time(foobar);", c, err)
+}
diff --git a/src/parser/parser.go b/src/parser/parser.go
index 19d27a955f..1ca79d6349 100644
--- a/src/parser/parser.go
+++ b/src/parser/parser.go
@@ -5,6 +5,7 @@ package parser
 import "C"
 
 import (
+	"common"
 	"fmt"
 	"time"
 	"unsafe"
@@ -39,17 +40,24 @@ type BoolExpression struct {
 
 type GroupByClause []*Value
 
-func (self GroupByClause) GetGroupByTime() (time.Duration, bool) {
+func (self GroupByClause) GetGroupByTime() (*time.Duration, error) {
 	for _, groupBy := range self {
 		if groupBy.IsFunctionCall() {
 			// TODO: check the number of arguments and return an error
+			if len(groupBy.Elems) != 1 {
+				return nil, common.NewQueryError(common.WrongNumberOfArguments, "time function only accepts one argument")
+			}
 			// TODO: check the function name
 			// TODO: error checking
-			duration, _ := time.ParseDuration(groupBy.Elems[0].Name)
-			return duration, true
+			arg := groupBy.Elems[0].Name
+			duration, err := time.ParseDuration(arg)
+			if err != nil {
+				return nil, common.NewQueryError(common.InvalidArgument, fmt.Sprintf("invalid argument %s to the time function", arg))
+			}
+			return &duration, nil
 		}
 	}
-	return 0, false
+	return nil, nil
 }
 
 type WhereCondition struct {