diff --git a/go.mod b/go.mod
index 652c717d3..e4ad72f65 100644
--- a/go.mod
+++ b/go.mod
@@ -10,7 +10,7 @@ require (
 	github.com/elastic/go-elasticsearch/v7 v7.9.0
 	github.com/elastic/go-licenser v0.3.1
 	github.com/elastic/go-ucfg v0.8.3
-	github.com/elastic/package-spec/code/go v0.0.0-20210622082315-342d612eb2a9
+	github.com/elastic/package-spec/code/go v0.0.0-20210623152222-b358e974b7f9
 	github.com/fatih/color v1.10.0
 	github.com/go-git/go-billy/v5 v5.0.0
 	github.com/go-git/go-git/v5 v5.1.0
diff --git a/go.sum b/go.sum
index 6e43c1c55..78b046cf3 100644
--- a/go.sum
+++ b/go.sum
@@ -204,8 +204,8 @@ github.com/elastic/go-licenser v0.3.1 h1:RmRukU/JUmts+rpexAw0Fvt2ly7VVu6mw8z4HrE
 github.com/elastic/go-licenser v0.3.1/go.mod h1:D8eNQk70FOCVBl3smCGQt/lv7meBeQno2eI1S5apiHQ=
 github.com/elastic/go-ucfg v0.8.3 h1:leywnFjzr2QneZZWhE6uWd+QN/UpP0sdJRHYyuFvkeo=
 github.com/elastic/go-ucfg v0.8.3/go.mod h1:iaiY0NBIYeasNgycLyTvhJftQlQEUO2hpF+FX0JKxzo=
-github.com/elastic/package-spec/code/go v0.0.0-20210622082315-342d612eb2a9 h1:Q6hJeu5XL7C65QIW6OTYYF7ViyedrTfu6QnFW9xppjk=
-github.com/elastic/package-spec/code/go v0.0.0-20210622082315-342d612eb2a9/go.mod h1:t0uvhLQGg3D4iQ5lSQEQs4YYS53MIIS05v0zm0fIBPM=
+github.com/elastic/package-spec/code/go v0.0.0-20210623152222-b358e974b7f9 h1:qvoqy6W/mhBY1t4xxP82oy34VTeF+MEqfVLiIGNBsEs=
+github.com/elastic/package-spec/code/go v0.0.0-20210623152222-b358e974b7f9/go.mod h1:t0uvhLQGg3D4iQ5lSQEQs4YYS53MIIS05v0zm0fIBPM=
 github.com/elazarl/goproxy v0.0.0-20180725130230-947c36da3153 h1:yUdfgN0XgIJw7foRItutHYUIhlcKzcSf5vDpdhQAKTc=
 github.com/elazarl/goproxy v0.0.0-20180725130230-947c36da3153/go.mod h1:/Zj4wYkgs4iZTTu3o/KG3Itv/qCCa8VVMlb3i9OVuzc=
 github.com/emicklei/go-restful v0.0.0-20170410110728-ff4f55a20633/go.mod h1:otzb+WCGbkyDHkqmQmT5YD2WR4BBwUdeQoFo8l/7tVs=
diff --git a/internal/fields/model.go b/internal/fields/model.go
index 0795a33f3..e351cda46 100644
--- a/internal/fields/model.go
+++ b/internal/fields/model.go
@@ -9,6 +9,7 @@ type FieldDefinition struct {
 	Name        string            `yaml:"name"`
 	Description string            `yaml:"description"`
 	Type        string            `yaml:"type"`
+	Value       string            `yaml:"value"` // The value to associate with a constant_keyword field.
 	Pattern     string            `yaml:"pattern"`
 	Unit        string            `yaml:"unit"`
 	MetricType  string            `yaml:"metric_type"`
diff --git a/internal/fields/testdata/constant-keyword-invalid.json b/internal/fields/testdata/constant-keyword-invalid.json
new file mode 100644
index 000000000..78f6c7bf8
--- /dev/null
+++ b/internal/fields/testdata/constant-keyword-invalid.json
@@ -0,0 +1,5 @@
+{
+  "foo": {
+    "constant": "wrong"
+  }
+}
\ No newline at end of file
diff --git a/internal/fields/testdata/constant-keyword-valid.json b/internal/fields/testdata/constant-keyword-valid.json
new file mode 100644
index 000000000..bda64f28e
--- /dev/null
+++ b/internal/fields/testdata/constant-keyword-valid.json
@@ -0,0 +1,5 @@
+{
+  "foo": {
+    "constant": "correct"
+  }
+}
\ No newline at end of file
diff --git a/internal/fields/testdata/fields/fields.yml b/internal/fields/testdata/fields/fields.yml
index 909d5260f..054de0965 100644
--- a/internal/fields/testdata/fields/fields.yml
+++ b/internal/fields/testdata/fields/fields.yml
@@ -8,3 +8,6 @@
       fields:
         - name: request_parameters
           type: flattened
+    - name: constant
+      type: constant_keyword
+      value: correct
diff --git a/internal/fields/validate.go b/internal/fields/validate.go
index f1259062c..0ebed23d3 100644
--- a/internal/fields/validate.go
+++ b/internal/fields/validate.go
@@ -293,19 +293,28 @@ func (v *Validator) parseElementValue(key string, definition FieldDefinition, va
 
 	var valid bool
 	switch definition.Type {
-	case "date", "ip", "constant_keyword", "keyword", "text":
+	case "constant_keyword":
 		var valStr string
 		valStr, valid = val.(string)
-		if !valid || definition.Pattern == "" {
+		if !valid {
 			break
 		}
 
-		valid, err := regexp.MatchString(definition.Pattern, valStr)
-		if err != nil {
-			return errors.Wrap(err, "invalid pattern")
+		if err := ensureConstantKeywordValueMatches(key, valStr, definition.Value); err != nil {
+			return err
+		}
+		if err := ensurePatternMatches(key, valStr, definition.Pattern); err != nil {
+			return err
 		}
+	case "date", "ip", "keyword", "text":
+		var valStr string
+		valStr, valid = val.(string)
 		if !valid {
-			return fmt.Errorf("field %q's value, %s, does not match the expected pattern: %s", key, valStr, definition.Pattern)
+			break
+		}
+
+		if err := ensurePatternMatches(key, valStr, definition.Pattern); err != nil {
+			return err
 		}
 	case "float", "long", "double":
 		_, valid = val.(float64)
@@ -331,3 +340,31 @@ func ensureSingleElementValue(val interface{}) (interface{}, bool) {
 	}
 	return nil, false // false: empty array, can't deduce single value type
 }
+
+// ensurePatternMatches validates the document's field value matches the field
+// definitions regular expression pattern.
+func ensurePatternMatches(key, value, pattern string) error {
+	if pattern == "" {
+		return nil
+	}
+	valid, err := regexp.MatchString(pattern, value)
+	if err != nil {
+		return errors.Wrap(err, "invalid pattern")
+	}
+	if !valid {
+		return fmt.Errorf("field %q's value, %s, does not match the expected pattern: %s", key, value, pattern)
+	}
+	return nil
+}
+
+// ensureConstantKeywordValueMatches validates the document's field value
+// matches the definition's constant_keyword value.
+func ensureConstantKeywordValueMatches(key, value, constantKeywordValue string) error {
+	if constantKeywordValue == "" {
+		return nil
+	}
+	if value != constantKeywordValue {
+		return fmt.Errorf("field %q's value %q does not match the declared constant_keyword value %q", key, value, constantKeywordValue)
+	}
+	return nil
+}
diff --git a/internal/fields/validate_test.go b/internal/fields/validate_test.go
index 92423e406..9bfa18218 100644
--- a/internal/fields/validate_test.go
+++ b/internal/fields/validate_test.go
@@ -61,6 +61,20 @@ func TestValidate_WithNumericKeywordFields(t *testing.T) {
 	require.Empty(t, errs)
 }
 
+func TestValidate_constant_keyword(t *testing.T) {
+	validator, err := CreateValidatorForDataStream("testdata")
+	require.NoError(t, err)
+	require.NotNil(t, validator)
+
+	e := readSampleEvent(t, "testdata/constant-keyword-invalid.json")
+	errs := validator.ValidateDocumentBody(e)
+	require.NotEmpty(t, errs)
+
+	e = readSampleEvent(t, "testdata/constant-keyword-valid.json")
+	errs = validator.ValidateDocumentBody(e)
+	require.Empty(t, errs)
+}
+
 func Test_parseElementValue(t *testing.T) {
 	for _, test := range []struct {
 		key        string