Check assignability

mapstructure.go

diff --git a/mapstructure.go b/mapstructure.go
index d4a49ed..f1a0c80 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -2,6 +2,7 @@
 
 import (
 	"errors"
+	"fmt"
 	"reflect"
 	"strings"
 )
@@ -60,6 +61,15 @@
 			panic("map value is not valid")
 		}
 
+		mapValType := mapVal.Type()
+		if !mapValType.AssignableTo(field.Type()) {
+			// If the value in the map can't be assigned to the field
+			// in the struct, then this is a problem...
+			return fmt.Errorf(
+				"field '%s' expected type '%s', got '%s'",
+				fieldName, field.Type(), mapValType)
+		}
+
 		field.Set(mapVal)
 	}
 

mapstructure_test.go

diff --git a/mapstructure_test.go b/mapstructure_test.go
index ec47e70..3ec2a3a 100644
--- a/mapstructure_test.go
+++ b/mapstructure_test.go
@@ -4,8 +4,9 @@
 
 type Basic struct {
 	Vstring string
-	Vint int
-	Vbool bool
+	Vint    int
+	Vbool   bool
+	Vextra  string
 }
 
 func TestBasicTypes(t *testing.T) {
@@ -13,8 +14,8 @@
 
 	input := map[string]interface{}{
 		"vstring": "foo",
-		"vint": 42,
-		"vbool": true,
+		"vint":    42,
+		"vbool":   true,
 	}
 
 	var result Basic
@@ -35,6 +36,29 @@
 	if result.Vbool != true {
 		t.Errorf("vbool value should be true: %#v", result.Vbool)
 	}
+
+	if result.Vextra != "" {
+		t.Errorf("vextra value should be empty: %#v", result.Vextra)
+	}
+}
+
+func TestInvalidType(t *testing.T) {
+	t.Parallel()
+
+	input := map[string]interface{}{
+		"vstring": 42,
+	}
+
+	var result Basic
+	err := MapToStruct(input, &result)
+	if err == nil {
+		t.Error("error should exist")
+		t.FailNow()
+	}
+
+	if err.Error() != "field 'Vstring' expected type 'string', got 'int'" {
+		t.Errorf("got unexpected error: %s", err)
+	}
 }
 
 func TestNonPtrValue(t *testing.T) {