diff --git a/conf.v b/conf.v
index 3ebc194..c7a0e0d 100644
--- a/conf.v
+++ b/conf.v
@@ -4,16 +4,25 @@ import os
 import toml
 import datatypes { Set }
 
+[params]
+pub struct LoadConfig {
+	prefix       string
+	file_suffix  string = '_FILE'
+	default_path string
+	// Allows overwriting
+	env map[string]string = os.environ()
+}
+
 // get_env_var tries to read the contents of the given environment variable. It
 // looks for either `${env.prefix}${field_name.to_upper()}` or
 // `${env.prefix}${field_name.to_upper()}${env.file_suffix}`, returning the
 // contents of the file instead if the latter. If both or neither exist, the
 // function returns an error.
-fn get_env_var(prefix string, field_name string, file_suffix string) !string {
-	env_var_name := '$prefix$field_name.to_upper()'
-	env_file_name := '$prefix$field_name.to_upper()$file_suffix'
-	env_var := os.getenv(env_var_name)
-	env_file := os.getenv(env_file_name)
+fn (ld LoadConfig) get_env_var(field_name string) !string {
+	env_var_name := '$ld.prefix$field_name.to_upper()'
+	env_file_name := '$ld.prefix$field_name.to_upper()$ld.file_suffix'
+	env_var := ld.env[env_var_name] or { '' }
+	env_file := ld.env[env_file_name] or { '' }
 
 	// If both are missing, we return an empty string
 	if env_var == '' && env_file == '' {
@@ -39,18 +48,11 @@ fn get_env_var(prefix string, field_name string, file_suffix string) !string {
 	}
 }
 
-[params]
-pub struct LoadConfig {
-	prefix       string
-	file_suffix  string = '_FILE'
-	default_path string
-}
-
 // load<T> attempts to create an object of type T from the given path to a toml
 // file & environment variables. For each field, it will select either a value
 // given from an environment variable, a value defined in the config file or a
 // configured default if present, in that order.
-pub fn load<T>(conf LoadConfig) !T {
+pub fn load<T>(ld LoadConfig) !T {
 	mut res := T{}
 
 	// This array allows us to determine later whether the variable is actually
@@ -58,7 +60,7 @@ pub fn load<T>(conf LoadConfig) !T {
 	mut has_value := Set<string>{}
 
 	// Later, this could be read from an env var as well.
-	path := conf.default_path
+	path := ld.default_path
 
 	if os.exists(path) {
 		// We don't use reflect here because reflect also sets any fields not
@@ -84,7 +86,7 @@ pub fn load<T>(conf LoadConfig) !T {
 	}
 
 	$for field in T.fields {
-		env_value := get_env_var(conf.prefix, field.name, conf.file_suffix)!
+		env_value := ld.get_env_var(field.name)!
 
 		// The value of an env var will always take precedence over the toml
 		// file.
@@ -117,12 +119,11 @@ pub fn load<T>(conf LoadConfig) !T {
 			}
 		}
 
-        // If there's no value provided in any way, we notify the user with an
-        // error.
+		// If there's no value provided in any way, we notify the user with an
+		// error.
 		if !has_value.exists(field.name) {
 			return error("Missing config variable '$field.name' with no provided default. Either add it to the config file or provide it using an environment variable.")
 		}
 	}
-
 	return res
 }
diff --git a/string_test.v b/string_test.v
index c498b11..b91cff5 100644
--- a/string_test.v
+++ b/string_test.v
@@ -8,6 +8,14 @@ struct SingleConfDefault {
 	some_string string = 'default'
 }
 
+const env = {
+	'SOME_STRING': 'env'
+}
+
+const prefix_env = {
+	'TEST_SOME_STRING': 'env'
+}
+
 fn test_string_present_no_default() {
 	conf := load<SingleConf>(default_path: 'test/string.toml')!
 	assert conf == SingleConf{
@@ -15,11 +23,35 @@ fn test_string_present_no_default() {
 	}
 }
 
+fn test_string_present_no_default_env() {
+	conf := load<SingleConf>(default_path: 'test/string.toml', env: .env)!
+	assert conf == SingleConf{
+		some_string: 'env'
+	}
+
+	conf2 := load<SingleConf>(default_path: 'test/string.toml', env: .prefix_env, prefix: 'TEST_')!
+	assert conf2 == SingleConf{
+		some_string: 'env'
+	}
+}
+
 fn test_string_absent_no_default() {
 	conf := load<SingleConf>(default_path: 'test/empty.toml') or { return }
 	assert false
 }
 
+fn test_string_absent_no_default_env() {
+	conf := load<SingleConf>(default_path: 'test/string.toml', env: .env)!
+	assert conf == SingleConf{
+		some_string: 'env'
+	}
+
+	conf2 := load<SingleConf>(default_path: 'test/string.toml', env: .prefix_env, prefix: 'TEST_')!
+	assert conf2 == SingleConf{
+		some_string: 'env'
+	}
+}
+
 fn test_string_present_default() {
 	conf := load<SingleConfDefault>(default_path: 'test/string.toml')!
 	assert conf == SingleConfDefault{
@@ -27,9 +59,41 @@ fn test_string_present_default() {
 	}
 }
 
+fn test_string_present_default_env() {
+	conf := load<SingleConfDefault>(default_path: 'test/string.toml', env: .env)!
+	assert conf == SingleConfDefault{
+		some_string: 'env'
+	}
+
+	conf2 := load<SingleConfDefault>(
+		default_path: 'test/string.toml'
+		env: .prefix_env
+		prefix: 'TEST_'
+	)!
+	assert conf2 == SingleConfDefault{
+		some_string: 'env'
+	}
+}
+
 fn test_string_absent_default() {
 	conf := load<SingleConfDefault>(default_path: 'test/empty.toml')!
 	assert conf == SingleConfDefault{
 		some_string: 'default'
 	}
 }
+
+fn test_string_absent_default_env() {
+	conf := load<SingleConfDefault>(default_path: 'test/empty.toml', env: .env)!
+	assert conf == SingleConfDefault{
+		some_string: 'env'
+	}
+
+	conf2 := load<SingleConfDefault>(
+		default_path: 'test/empty.toml'
+		env: .prefix_env
+		prefix: 'TEST_'
+	)!
+	assert conf2 == SingleConfDefault{
+		some_string: 'env'
+	}
+}