diff --git a/helper/schema/schema.go b/helper/schema/schema.go
index a6e3a3f22..3e16bb3ab 100644
--- a/helper/schema/schema.go
+++ b/helper/schema/schema.go
@@ -2,6 +2,7 @@ package schema
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/mitchellh/mapstructure"
@@ -104,20 +105,7 @@ func (m schemaMap) Diff(
 
 // Validate validates the configuration against this schema mapping.
 func (m schemaMap) Validate(c *terraform.ResourceConfig) ([]string, []error) {
-	var ws []string
-	var es []error
-
-	for k, schema := range m {
-		ws2, es2 := m.validate(k, schema, c)
-		if len(ws2) > 0 {
-			ws = append(ws, ws2...)
-		}
-		if len(es2) > 0 {
-			es = append(es, es2...)
-		}
-	}
-
-	return ws, es
+	return m.validateObject("", m, c)
 }
 
 func (m schemaMap) diff(
@@ -345,9 +333,12 @@ func (m schemaMap) validateObject(
 	var ws []string
 	var es []error
 	for subK, s := range schema {
-		key := fmt.Sprintf("%s.%s", k, subK)
-		ws2, es2 := m.validate(key, s, c)
+		key := subK
+		if k != "" {
+			key = fmt.Sprintf("%s.%s", k, subK)
+		}
 
+		ws2, es2 := m.validate(key, s, c)
 		if len(ws2) > 0 {
 			ws = append(ws, ws2...)
 		}
@@ -356,6 +347,23 @@ func (m schemaMap) validateObject(
 		}
 	}
 
+	// Detect any extra/unknown keys and report those as errors.
+	prefix := k + "."
+	for configK, _ := range c.Raw {
+		if k != "" {
+			if !strings.HasPrefix(configK, prefix) {
+				continue
+			}
+
+			configK = configK[len(prefix):]
+		}
+
+		if _, ok := schema[configK]; !ok {
+			es = append(es, fmt.Errorf(
+				"%s: invalid or unknown key: %s", k, configK))
+		}
+	}
+
 	return ws, es
 }
 
diff --git a/helper/schema/schema_test.go b/helper/schema/schema_test.go
index 10f4f3d7e..66d70bb52 100644
--- a/helper/schema/schema_test.go
+++ b/helper/schema/schema_test.go
@@ -604,6 +604,24 @@ func TestSchemaMap_Validate(t *testing.T) {
 
 			Err: false,
 		},
+
+		// Invalid/unknown field
+		{
+			Schema: map[string]*Schema{
+				"availability_zone": &Schema{
+					Type:     TypeString,
+					Optional: true,
+					Computed: true,
+					ForceNew: true,
+				},
+			},
+
+			Config: map[string]interface{}{
+				"foo": "bar",
+			},
+
+			Err: true,
+		},
 	}
 
 	for i, tc := range cases {