diff --git a/config/config.go b/config/config.go
index 290fa2d9c..01dfee3b2 100644
--- a/config/config.go
+++ b/config/config.go
@@ -17,6 +17,7 @@ import (
 	"errors"
 	"fmt"
 	"github.com/prometheus/prometheus/model"
+	"github.com/prometheus/prometheus/utility"
 	"time"
 )
 
@@ -55,7 +56,7 @@ func (config *Config) AddJob(options map[string]string, targets []Targets) error
 		return errors.New("Missing job name")
 	}
 	if len(targets) == 0 {
-		return errors.New(fmt.Sprintf("No targets configured for job '%v'", name))
+		return fmt.Errorf("No targets configured for job '%v'", name)
 	}
 	job := &JobConfig{
 		Targets: tmpJobTargets,
@@ -69,18 +70,18 @@ func (config *Config) AddJob(options map[string]string, targets []Targets) error
 	return nil
 }
 
-func (config *GlobalConfig) SetOption(option string, value string) error {
+func (config *GlobalConfig) SetOption(option string, value string) (err error) {
 	switch option {
 	case "scrape_interval":
-		config.ScrapeInterval = stringToDuration(value)
+		config.ScrapeInterval, err = utility.StringToDuration(value)
 		return nil
 	case "evaluation_interval":
-		config.EvaluationInterval = stringToDuration(value)
-		return nil
+		config.EvaluationInterval, err = utility.StringToDuration(value)
+		return err
 	default:
-		return errors.New(fmt.Sprintf("Unrecognized global configuration option '%v'", option))
+		err = fmt.Errorf("Unrecognized global configuration option '%v'", option)
 	}
-	return nil
+	return
 }
 
 func (config *GlobalConfig) SetLabels(labels model.LabelSet) {
@@ -95,18 +96,16 @@ func (config *GlobalConfig) AddRuleFiles(ruleFiles []string) {
 	}
 }
 
-func (job *JobConfig) SetOption(option string, value string) error {
+func (job *JobConfig) SetOption(option string, value string) (err error) {
 	switch option {
 	case "name":
 		job.Name = value
-		return nil
 	case "scrape_interval":
-		job.ScrapeInterval = stringToDuration(value)
-		return nil
+		job.ScrapeInterval, err = utility.StringToDuration(value)
 	default:
-		return errors.New(fmt.Sprintf("Unrecognized job configuration option '%v'", option))
+		err = fmt.Errorf("Unrecognized job configuration option '%v'", option)
 	}
-	return nil
+	return
 }
 
 func (job *JobConfig) AddTargets(endpoints []string, labels model.LabelSet) {
diff --git a/config/helpers.go b/config/helpers.go
index af7251969..8ef989345 100644
--- a/config/helpers.go
+++ b/config/helpers.go
@@ -17,9 +17,6 @@ import (
 	"fmt"
 	"github.com/prometheus/prometheus/model"
 	"log"
-	"regexp"
-	"strconv"
-	"time"
 )
 
 // Unfortunately, more global variables that are needed for parsing.
@@ -30,7 +27,9 @@ var tmpTargetLabels = model.LabelSet{}
 
 func configError(error string, v ...interface{}) {
 	message := fmt.Sprintf(error, v...)
-	log.Fatal(fmt.Sprintf("Line %v, char %v: %s", yyline, yypos, message))
+	// TODO: Don't just die here. Pass errors back all the way to the caller
+	// instead.
+	log.Fatalf("Line %v, char %v: %s", yyline, yypos, message)
 }
 
 func PushJobOption(option string, value string) {
@@ -66,26 +65,3 @@ func PopJob() {
 	tmpJobOptions = map[string]string{}
 	tmpJobTargets = []Targets{}
 }
-
-func stringToDuration(durationStr string) time.Duration {
-	durationRE := regexp.MustCompile("^([0-9]+)([ywdhms]+)$")
-	matches := durationRE.FindStringSubmatch(durationStr)
-	if len(matches) != 3 {
-		configError("Not a valid duration string: '%v'", durationStr)
-	}
-	value, _ := strconv.Atoi(matches[1])
-	unit := matches[2]
-	switch unit {
-	case "y":
-		value *= 60 * 60 * 24 * 365
-	case "w":
-		value *= 60 * 60 * 24 * 7
-	case "d":
-		value *= 60 * 60 * 24
-	case "h":
-		value *= 60 * 60
-	case "m":
-		value *= 60
-	}
-	return time.Duration(value) * time.Second
-}
diff --git a/config/printer.go b/config/printer.go
index 26d7c6bc1..00e4c7dc1 100644
--- a/config/printer.go
+++ b/config/printer.go
@@ -16,6 +16,7 @@ package config
 import (
 	"fmt"
 	"github.com/prometheus/prometheus/model"
+	"github.com/prometheus/prometheus/utility"
 	"strings"
 )
 
@@ -47,8 +48,8 @@ func labelsToString(indent int, labels model.LabelSet) string {
 
 func (global *GlobalConfig) ToString(indent int) string {
 	str := indentStr(indent, "global {\n")
-	str += indentStr(indent+1, "scrape_interval = \"%vs\"\n", global.ScrapeInterval)
-	str += indentStr(indent+1, "evaluation_interval = \"%vs\"\n", global.EvaluationInterval)
+	str += indentStr(indent+1, "scrape_interval = \"%s\"\n", utility.DurationToString(global.ScrapeInterval))
+	str += indentStr(indent+1, "evaluation_interval = \"%s\"\n", utility.DurationToString(global.EvaluationInterval))
 	str += labelsToString(indent+1, global.Labels)
 	str += indentStr(indent, "}\n")
 	str += indentStr(indent+1, "rule_files = [\n")
@@ -61,9 +62,8 @@ func (global *GlobalConfig) ToString(indent int) string {
 
 func (job *JobConfig) ToString(indent int) string {
 	str := indentStr(indent, "job {\n")
-	str += indentStr(indent+1, "job {\n")
 	str += indentStr(indent+1, "name = \"%v\"\n", job.Name)
-	str += indentStr(indent+1, "scrape_interval = \"%vs\"\n", job.ScrapeInterval)
+	str += indentStr(indent+1, "scrape_interval = \"%s\"\n", utility.DurationToString(job.ScrapeInterval))
 	for _, targets := range job.Targets {
 		str += indentStr(indent+1, "targets {\n")
 		str += indentStr(indent+2, "endpoints = [\n")
diff --git a/rules/ast/printer.go b/rules/ast/printer.go
index 1f38117ac..4fd16296d 100644
--- a/rules/ast/printer.go
+++ b/rules/ast/printer.go
@@ -16,6 +16,7 @@ package ast
 import (
 	"encoding/json"
 	"fmt"
+	"github.com/prometheus/prometheus/utility"
 	"sort"
 	"strings"
 	"time"
@@ -65,29 +66,6 @@ func exprTypeToString(exprType ExprType) string {
 	return exprTypeMap[exprType]
 }
 
-func durationToString(duration time.Duration) string {
-	seconds := int64(duration / time.Second)
-	factors := map[string]int64{
-		"y": 60 * 60 * 24 * 365,
-		"d": 60 * 60 * 24,
-		"h": 60 * 60,
-		"m": 60,
-		"s": 1,
-	}
-	unit := "s"
-	switch int64(0) {
-	case seconds % factors["y"]:
-		unit = "y"
-	case seconds % factors["d"]:
-		unit = "d"
-	case seconds % factors["h"]:
-		unit = "h"
-	case seconds % factors["m"]:
-		unit = "m"
-	}
-	return fmt.Sprintf("%v%v", seconds/factors[unit], unit)
-}
-
 func (vector Vector) ToString() string {
 	metricStrings := []string{}
 	for _, sample := range vector {
@@ -228,7 +206,7 @@ func (node *VectorLiteral) ToString() string {
 
 func (node *MatrixLiteral) ToString() string {
 	vectorString := (&VectorLiteral{labels: node.labels}).ToString()
-	intervalString := fmt.Sprintf("['%v']", durationToString(node.interval))
+	intervalString := fmt.Sprintf("['%v']", utility.DurationToString(node.interval))
 	return vectorString + intervalString
 }
 
diff --git a/rules/helpers.go b/rules/helpers.go
index 3008768d1..a5a224c44 100644
--- a/rules/helpers.go
+++ b/rules/helpers.go
@@ -14,48 +14,15 @@
 package rules
 
 import (
-	"errors"
 	"fmt"
 	"github.com/prometheus/prometheus/model"
 	"github.com/prometheus/prometheus/rules/ast"
-	"regexp"
-	"strconv"
-	"time"
+	"github.com/prometheus/prometheus/utility"
 )
 
-func rulesError(error string, v ...interface{}) error {
-	return errors.New(fmt.Sprintf(error, v...))
-}
-
-// TODO move to common place, currently duplicated in config/
-func stringToDuration(durationStr string) (time.Duration, error) {
-	durationRE := regexp.MustCompile("^([0-9]+)([ywdhms]+)$")
-	matches := durationRE.FindStringSubmatch(durationStr)
-	if len(matches) != 3 {
-		return 0, rulesError("Not a valid duration string: '%v'", durationStr)
-	}
-	value, _ := strconv.Atoi(matches[1])
-	unit := matches[2]
-	switch unit {
-	case "y":
-		value *= 60 * 60 * 24 * 365
-	case "w":
-		value *= 60 * 60 * 24
-	case "d":
-		value *= 60 * 60 * 24
-	case "h":
-		value *= 60 * 60
-	case "m":
-		value *= 60
-	case "s":
-		value *= 1
-	}
-	return time.Duration(value) * time.Second, nil
-}
-
 func CreateRule(name string, labels model.LabelSet, root ast.Node, permanent bool) (*Rule, error) {
 	if root.Type() != ast.VECTOR {
-		return nil, rulesError("Rule %v does not evaluate to vector type", name)
+		return nil, fmt.Errorf("Rule %v does not evaluate to vector type", name)
 	}
 	return NewRule(name, labels, root.(ast.VectorNode), permanent), nil
 }
@@ -63,18 +30,18 @@ func CreateRule(name string, labels model.LabelSet, root ast.Node, permanent boo
 func NewFunctionCall(name string, args []ast.Node) (ast.Node, error) {
 	function, err := ast.GetFunction(name)
 	if err != nil {
-		return nil, rulesError("Unknown function \"%v\"", name)
+		return nil, fmt.Errorf("Unknown function \"%v\"", name)
 	}
 	functionCall, err := ast.NewFunctionCall(function, args)
 	if err != nil {
-		return nil, rulesError(err.Error())
+		return nil, fmt.Errorf(err.Error())
 	}
 	return functionCall, nil
 }
 
 func NewVectorAggregation(aggrTypeStr string, vector ast.Node, groupBy []model.LabelName) (*ast.VectorAggregation, error) {
 	if vector.Type() != ast.VECTOR {
-		return nil, rulesError("Operand of %v aggregation must be of vector type", aggrTypeStr)
+		return nil, fmt.Errorf("Operand of %v aggregation must be of vector type", aggrTypeStr)
 	}
 	var aggrTypes = map[string]ast.AggrType{
 		"SUM": ast.SUM,
@@ -84,7 +51,7 @@ func NewVectorAggregation(aggrTypeStr string, vector ast.Node, groupBy []model.L
 	}
 	aggrType, ok := aggrTypes[aggrTypeStr]
 	if !ok {
-		return nil, rulesError("Unknown aggregation type '%v'", aggrTypeStr)
+		return nil, fmt.Errorf("Unknown aggregation type '%v'", aggrTypeStr)
 	}
 	return ast.NewVectorAggregation(aggrType, vector.(ast.VectorNode), groupBy), nil
 }
@@ -107,11 +74,11 @@ func NewArithExpr(opTypeStr string, lhs ast.Node, rhs ast.Node) (ast.Node, error
 	}
 	opType, ok := opTypes[opTypeStr]
 	if !ok {
-		return nil, rulesError("Invalid binary operator \"%v\"", opTypeStr)
+		return nil, fmt.Errorf("Invalid binary operator \"%v\"", opTypeStr)
 	}
 	expr, err := ast.NewArithExpr(opType, lhs, rhs)
 	if err != nil {
-		return nil, rulesError(err.Error())
+		return nil, fmt.Errorf(err.Error())
 	}
 	return expr, nil
 }
@@ -123,9 +90,9 @@ func NewMatrix(vector ast.Node, intervalStr string) (ast.MatrixNode, error) {
 			break
 		}
 	default:
-		return nil, rulesError("Intervals are currently only supported for vector literals.")
+		return nil, fmt.Errorf("Intervals are currently only supported for vector literals.")
 	}
-	interval, err := stringToDuration(intervalStr)
+	interval, err := utility.StringToDuration(intervalStr)
 	if err != nil {
 		return nil, err
 	}
diff --git a/rules/lexer.l b/rules/lexer.l
index f174f0bbf..643f52fc6 100644
--- a/rules/lexer.l
+++ b/rules/lexer.l
@@ -48,7 +48,9 @@ AVG|SUM|MAX|MIN          { yylval.str = yytext; return AGGR_OP }
 {L}({L}|{D})+            { yylval.str = yytext; return IDENTIFIER }
 
 \-?{D}+(\.{D}*)?         { num, err := strconv.ParseFloat(yytext, 32);
-                           if (err != nil) { rulesError("Invalid float %v", yytext) }
+                           if (err != nil && err.(*strconv.NumError).Err == strconv.ErrSyntax) {
+                             panic("Invalid float")
+                           }
                            yylval.num = model.SampleValue(num)
                            return NUMBER }
 
diff --git a/rules/lexer.l.go b/rules/lexer.l.go
index aceeaec4a..7ec712fd6 100644
--- a/rules/lexer.l.go
+++ b/rules/lexer.l.go
@@ -436,8 +436,8 @@ var yyrules []yyrule = []yyrule{{regexp.MustCompile("[^\\n]"), nil, []yystartcon
 	}()
 	{
 		num, err := strconv.ParseFloat(yytext, 32)
-		if err != nil {
-			rulesError("Invalid float %v", yytext)
+		if err != nil && err.(*strconv.NumError).Err == strconv.ErrSyntax {
+			panic("Invalid float")
 		}
 		yylval.num = model.SampleValue(num)
 		return yyactionreturn{NUMBER, yyRT_USER_RETURN}
diff --git a/utility/strconv.go b/utility/strconv.go
new file mode 100644
index 000000000..655395f87
--- /dev/null
+++ b/utility/strconv.go
@@ -0,0 +1,72 @@
+// Copyright 2013 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package utility
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"time"
+)
+
+var durationRE = regexp.MustCompile("^([0-9]+)([ywdhms]+)$")
+
+func DurationToString(duration time.Duration) string {
+	seconds := int64(duration / time.Second)
+	factors := map[string]int64{
+		"y": 60 * 60 * 24 * 365,
+		"d": 60 * 60 * 24,
+		"h": 60 * 60,
+		"m": 60,
+		"s": 1,
+	}
+	unit := "s"
+	switch int64(0) {
+	case seconds % factors["y"]:
+		unit = "y"
+	case seconds % factors["d"]:
+		unit = "d"
+	case seconds % factors["h"]:
+		unit = "h"
+	case seconds % factors["m"]:
+		unit = "m"
+	}
+	return fmt.Sprintf("%v%v", seconds/factors[unit], unit)
+}
+
+func StringToDuration(durationStr string) (duration time.Duration, err error) {
+	matches := durationRE.FindStringSubmatch(durationStr)
+	if len(matches) != 3 {
+		err = fmt.Errorf("Not a valid duration string: '%v'", durationStr)
+		return
+	}
+	durationSeconds, _ := strconv.Atoi(matches[1])
+	duration = time.Duration(durationSeconds) * time.Second
+	unit := matches[2]
+	switch unit {
+	case "y":
+		duration *= 60 * 60 * 24 * 365
+	case "w":
+		duration *= 60 * 60 * 24 * 7
+	case "d":
+		duration *= 60 * 60 * 24
+	case "h":
+		duration *= 60 * 60
+	case "m":
+		duration *= 60
+	case "s":
+		duration *= 1
+	}
+	return
+}