diff --git a/env.go b/env.go
index 61ffd2a..084dc12 100644
--- a/env.go
+++ b/env.go
@@ -201,11 +201,13 @@ func set(t reflect.Type, f reflect.Value, value string) error {
 			break
 		}
 
-		v, err := strconv.Atoi(value)
+		// Using ParseInt because strconv.Atoi returns int,
+		// which is not guaranteed to be 64-bit on all platforms
+		v, err := strconv.ParseInt(value, 10, 64)
 		if err != nil {
 			return err
 		}
-		f.SetInt(int64(v))
+		f.SetInt(v)
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
 		v, err := strconv.ParseUint(value, 10, 64)
 		if err != nil {
diff --git a/env_test.go b/env_test.go
index 3d120af..dfd3230 100644
--- a/env_test.go
+++ b/env_test.go
@@ -56,6 +56,7 @@ type ValidStruct struct {
 	Uint    uint    `env:"UINT"`
 	Float32 float32 `env:"FLOAT32"`
 	Float64 float64 `env:"FLOAT64"`
+	Int64   int64   `env:"INT64"`
 	Bool    bool    `env:"BOOL"`
 
 	MultipleTags string `env:"npm_config_cache,NPM_CONFIG_CACHE"`
@@ -146,6 +147,7 @@ func TestUnmarshal(t *testing.T) {
 		"UINT":             "4294967295",
 		"FLOAT32":          "2.3",
 		"FLOAT64":          "4.5",
+		"INT64":            "4294967296",
 		"BOOL":             "true",
 		"npm_config_cache": "first",
 		"NPM_CONFIG_CACHE": "second",
@@ -190,6 +192,10 @@ func TestUnmarshal(t *testing.T) {
 		t.Errorf("Expected field value to be '%f' but got '%f'", 4.5, validStruct.Float64)
 	}
 
+	if validStruct.Int64 != 4294967296 {
+		t.Errorf("Expected field value to be '%d' but got '%d'", int64(4294967296), validStruct.Int64)
+	}
+
 	if validStruct.Bool != true {
 		t.Errorf("Expected field value to be '%t' but got '%t'", true, validStruct.Bool)
 	}