diff --git a/builtins.go b/builtins.go
index 3dd9d92..8d977bc 100644
--- a/builtins.go
+++ b/builtins.go
@@ -17,7 +17,6 @@
 package validator
 
 import (
-	"errors"
 	"reflect"
 	"regexp"
 	"strconv"
@@ -46,7 +45,7 @@ func nonzero(v interface{}, param string) error {
 	case reflect.Invalid:
 		valid = false // always invalid
 	default:
-		panic("Unsupported type " + st.String())
+		return ErrUnsupported
 	}
 
 	if !valid {
@@ -63,17 +62,37 @@ func length(v interface{}, param string) error {
 	valid := true
 	switch st.Kind() {
 	case reflect.String:
-		valid = int64(len(st.String())) == asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		valid = int64(len(st.String())) == p
 	case reflect.Slice, reflect.Map, reflect.Array:
-		valid = int64(st.Len()) == asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		valid = int64(st.Len()) == p
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		valid = st.Int() == asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		valid = st.Int() == p
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		valid = st.Uint() == asUint(param)
+		p, err := asUint(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		valid = st.Uint() == p
 	case reflect.Float32, reflect.Float64:
-		valid = st.Float() == asFloat(param)
+		p, err := asFloat(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		valid = st.Float() == p
 	default:
-		panic("length is not a valid validation tag for type " + st.String())
+		return ErrUnsupported
 	}
 	if !valid {
 		return ErrLen
@@ -90,17 +109,37 @@ func min(v interface{}, param string) error {
 	invalid := false
 	switch st.Kind() {
 	case reflect.String:
-		invalid = int64(len(st.String())) < asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = int64(len(st.String())) < p
 	case reflect.Slice, reflect.Map, reflect.Array:
-		invalid = int64(st.Len()) < asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = int64(st.Len()) < p
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		invalid = st.Int() < asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Int() < p
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		invalid = st.Uint() < asUint(param)
+		p, err := asUint(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Uint() < p
 	case reflect.Float32, reflect.Float64:
-		invalid = st.Float() < asFloat(param)
+		p, err := asFloat(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Float() < p
 	default:
-		panic("min is not a valid validation tag for type " + st.String())
+		return ErrUnsupported
 	}
 	if invalid {
 		return ErrMin
@@ -117,17 +156,37 @@ func max(v interface{}, param string) error {
 	var invalid bool
 	switch st.Kind() {
 	case reflect.String:
-		invalid = int64(len(st.String())) > asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = int64(len(st.String())) > p
 	case reflect.Slice, reflect.Map, reflect.Array:
-		invalid = int64(st.Len()) > asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = int64(st.Len()) > p
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		invalid = st.Int() > asInt(param)
+		p, err := asInt(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Int() > p
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		invalid = st.Uint() > asUint(param)
+		p, err := asUint(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Uint() > p
 	case reflect.Float32, reflect.Float64:
-		invalid = st.Float() > asFloat(param)
+		p, err := asFloat(param)
+		if err != nil {
+			return ErrBadParameter
+		}
+		invalid = st.Float() > p
 	default:
-		panic("max is not a valid validation tag for type " + st.String())
+		return ErrUnsupported
 	}
 	if invalid {
 		return ErrMax
@@ -140,43 +199,46 @@ func max(v interface{}, param string) error {
 func regex(v interface{}, param string) error {
 	s, ok := v.(string)
 	if !ok {
-		panic("regexp requires a string")
+		return ErrUnsupported
 	}
 
-	re := regexp.MustCompile(param)
+	re, err := regexp.Compile(param)
+	if err != nil {
+		return ErrBadParameter
+	}
 
 	if !re.MatchString(s) {
-		return errors.New("regexp does not match")
+		return ErrRegexp
 	}
 	return nil
 }
 
 // asInt retuns the parameter as a int64
 // or panics if it can't convert
-func asInt(param string) int64 {
+func asInt(param string) (int64, error) {
 	i, err := strconv.ParseInt(param, 0, 64)
 	if err != nil {
-		panic("Invalid param " + param + ", should be an integer")
+		return 0, ErrBadParameter
 	}
-	return i
+	return i, nil
 }
 
 // asUint retuns the parameter as a uint64
 // or panics if it can't convert
-func asUint(param string) uint64 {
+func asUint(param string) (uint64, error) {
 	i, err := strconv.ParseUint(param, 0, 64)
 	if err != nil {
-		panic("Invalid param " + param + ", should be an unsigned integer")
+		return 0, ErrBadParameter
 	}
-	return i
+	return i, nil
 }
 
 // asFloat retuns the parameter as a float64
 // or panics if it can't convert
-func asFloat(param string) float64 {
+func asFloat(param string) (float64, error) {
 	i, err := strconv.ParseFloat(param, 64)
 	if err != nil {
-		panic("Invalid param " + param + ", should be a float")
+		return 0.0, ErrBadParameter
 	}
-	return i
+	return i, nil
 }
diff --git a/doc.go b/doc.go
index e1759f0..df2b55e 100644
--- a/doc.go
+++ b/doc.go
@@ -85,7 +85,7 @@ Note that there are no tests to prevent conflicting validator parameters. For
 instance, these fields will never be valid.
 
 	...
-	A int     `validate:"max=0,nonzero"`
+	A int     `validate:"max=0,min=1"`
 	B string  `validate:"len=10,regexp=^$"
 	...
 
@@ -98,7 +98,7 @@ First, one needs to create a validation function.
 	func notZZ(v interface{}, param string) error {
 		st := reflect.ValueOf(v)
 		if st.Kind() != reflect.String {
-			return errors.New("notZZ only validates strings")
+			return validate.ErrUnsupported
 		}
 		if st.String() == "ZZ" {
 			return errors.New("value cannot be ZZ")
@@ -127,7 +127,7 @@ To use parameters, it is very similar.
 	func notSomething(v interface{}, param string) error {
 		st := reflect.ValueOf(v)
 		if st.Kind() != reflect.String {
-			return errors.New("notSomething only validates strings")
+			return validate.ErrUnsupported
 		}
 		if st.String() == param {
 			return errors.New("value cannot be " + param)
@@ -155,7 +155,8 @@ And you can delete a validation function by setting it to nil.
 	validate.SetValidationFunc("notzz", nil)
 	validate.SetValidationFunc("nonzero", nil)
 
-Using a non-existing validation func in a field tag will panic.
+Using a non-existing validation func in a field tag will always return
+false and with error validate.ErrUnknownTag.
 
 Finally, package validator also provides a helper function that can be used
 to validate simple variables/values.
diff --git a/examplevalidate_test.go b/examplevalidate_test.go
index 8df81c8..2c04c07 100644
--- a/examplevalidate_test.go
+++ b/examplevalidate_test.go
@@ -70,7 +70,7 @@ func ExampleValidate() {
 	// Street cannot be empty.
 	// Invalid due to fields:
 	//	 - Age ([less than min])
-	//	 - Email ([regexp does not match])
+	//	 - Email ([regular expression mismatch])
 	//	 - Address.Street ([zero value])
 }
 
diff --git a/validator.go b/validator.go
index cc93d6c..f8e6623 100644
--- a/validator.go
+++ b/validator.go
@@ -35,9 +35,18 @@ var (
 	// ErrLen is the error returned when length is not equal to
 	// param specified
 	ErrLen = errors.New("invalid length")
+	// ErrRegexp is the error returned when the value does not
+	// match the provided regular expression parameter
+	ErrRegexp = errors.New("regular expression mismatch")
 	// ErrUnsupported is the error error returned when a validation rule
 	// is used with an unsupported variable type
 	ErrUnsupported = errors.New("unsupported type")
+	// ErrBadParameter is the error returned when an invalid parameter
+	// is provided to a validation rule (e.g. a string where an int was
+	// expected (max=foo,len=bar) or missing a parameter when one is required (len=))
+	ErrBadParameter = errors.New("bad parameter")
+	// ErrUnknownTag is the error returned when an unknown tag is found
+	ErrUnknownTag = errors.New("unknown tag")
 	// ErrInvalid is the error returned when variable is invalid
 	// (normally a nil pointer)
 	ErrInvalid = errors.New("invalid value")
@@ -219,7 +228,11 @@ func (mv *Validator) Valid(val interface{}, tags string) (bool, []error) {
 
 // validateVar validates one single variable
 func (mv *Validator) validateVar(v interface{}, tag string) []error {
-	tags := mv.parseTags(tag)
+	tags, err := mv.parseTags(tag)
+	if err != nil {
+		// unknown tag found, give up.
+		return []error{err}
+	}
 	errs := make([]error, 0, len(tags))
 	for _, t := range tags {
 		if err := t.Fn(v, t.Param); err != nil {
@@ -237,8 +250,7 @@ type tag struct {
 }
 
 // parseTags parses all individual tags found within a struct tag.
-// These usually are in the
-func (mv *Validator) parseTags(t string) []tag {
+func (mv *Validator) parseTags(t string) ([]tag, error) {
 	tl := strings.Split(t, ",")
 	tags := make([]tag, 0, len(tl))
 	for _, i := range tl {
@@ -246,18 +258,17 @@ func (mv *Validator) parseTags(t string) []tag {
 		v := strings.SplitN(i, "=", 2)
 		tg.Name = strings.Trim(v[0], " ")
 		if tg.Name == "" {
-			panic("empty tag")
+			return []tag{}, ErrUnknownTag
 		}
 		if len(v) > 1 {
 			tg.Param = strings.Trim(v[1], " ")
 		}
 		var found bool
 		if tg.Fn, found = mv.validationFuncs[tg.Name]; !found {
-			panic("invalid tag " + tg.Name)
+			return []tag{}, ErrUnknownTag
 		}
-
 		tags = append(tags, tg)
 
 	}
-	return tags
+	return tags, nil
 }
diff --git a/validator_test.go b/validator_test.go
index fa3a2fc..1871414 100644
--- a/validator_test.go
+++ b/validator_test.go
@@ -17,8 +17,8 @@
 package validator_test
 
 import (
-	. "gopkg.in/check.v1"
 	"testing"
+	. "gopkg.in/check.v1"
 
 	"gopkg.in/validator.v1"
 )
@@ -178,21 +178,44 @@ func (ms *MySuite) TestValidateStructVar(c *C) {
 	c.Assert(errs, HasError, validator.ErrUnsupported)
 }
 
-/*
-func (ms *MySuite) TestValidateVar1(c *C) {
-	t1 := TestStruct{Number: 123, Text: "Blah"}
+func (ms *MySuite) TestUnknownTag(c *C) {
+	type test struct {
+		A int `validate:"foo"`
+	}
+	t := test{}
+	valid, errs := validator.Validate(t)
+	c.Assert(valid, Equals, false)
+	c.Assert(errs, HasLen, 1)
+	c.Assert(errs["A"], HasError, validator.ErrUnknownTag)
+}
 
-	//s := reflect.ValueOf(t).Elem()
-	s := reflect.ValueOf(t1)
-	st := s.Type()
-	for i := 0; i < s.NumField(); i++ {
-		f := s.Field(i)
-		fmt.Printf("%d: %s %s %s = %v\n", i,
-			st.Field(i).Name, f.Type(), st.Field(i).Tag.Get("validator"), f.Interface())
+func (ms *MySuite) TestUnsupported(c *C) {
+	type test struct {
+		A int     `validate:"regexp=a.*b"`
+		B float64 `validate:"regexp=.*"`
 	}
+	t := test{}
+	valid, errs := validator.Validate(t)
+	c.Assert(valid, Equals, false)
+	c.Assert(errs, HasLen, 2)
+	c.Assert(errs["A"], HasError, validator.ErrUnsupported)
+	c.Assert(errs["B"], HasError, validator.ErrUnsupported)
+}
 
+func (ms *MySuite) TestBadParameter(c *C) {
+	type test struct {
+		A string `validate:"min="`
+		B string `validate:"len=="`
+		C string `validate:"max=foo"`
+	}
+	t := test{}
+	valid, errs := validator.Validate(t)
+	c.Assert(valid, Equals, false)
+	c.Assert(errs, HasLen, 3)
+	c.Assert(errs["A"], HasError, validator.ErrBadParameter)
+	c.Assert(errs["B"], HasError, validator.ErrBadParameter)
+	c.Assert(errs["C"], HasError, validator.ErrBadParameter)
 }
-*/
 
 type hasErrorChecker struct {
 	*CheckerInfo