diff --git a/altsrc/default_input_source.go b/altsrc/default_input_source.go
new file mode 100644
index 0000000000..7fda719be8
--- /dev/null
+++ b/altsrc/default_input_source.go
@@ -0,0 +1,6 @@
+package altsrc
+
+// defaultInputSource creates a default InputSourceContext.
+func defaultInputSource() (InputSourceContext, error) {
+	return &MapInputSource{file: "", valueMap: map[interface{}]interface{}{}}, nil
+}
diff --git a/altsrc/json_source_context.go b/altsrc/json_source_context.go
index 7d70a2a57a..6e7bf11f91 100644
--- a/altsrc/json_source_context.go
+++ b/altsrc/json_source_context.go
@@ -17,7 +17,11 @@ import (
 // by the given flag.
 func NewJSONSourceFromFlagFunc(flag string) func(c *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
-		return NewJSONSourceFromFile(context.String(flag))
+		if context.IsSet(flag) {
+			return NewJSONSourceFromFile(context.String(flag))
+		}
+
+		return defaultInputSource()
 	}
 }
 
diff --git a/altsrc/toml_file_loader.go b/altsrc/toml_file_loader.go
index c679fdbebc..9b86ee1a63 100644
--- a/altsrc/toml_file_loader.go
+++ b/altsrc/toml_file_loader.go
@@ -87,8 +87,12 @@ func NewTomlSourceFromFile(file string) (InputSourceContext, error) {
 // NewTomlSourceFromFlagFunc creates a new TOML InputSourceContext from a provided flag name and source context.
 func NewTomlSourceFromFlagFunc(flagFileName string) func(context *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
-		filePath := context.String(flagFileName)
-		return NewTomlSourceFromFile(filePath)
+		if context.IsSet(flagFileName) {
+			filePath := context.String(flagFileName)
+			return NewTomlSourceFromFile(filePath)
+		}
+
+		return defaultInputSource()
 	}
 }
 
diff --git a/altsrc/yaml_file_loader.go b/altsrc/yaml_file_loader.go
index cf2f8a5c55..a49df56f35 100644
--- a/altsrc/yaml_file_loader.go
+++ b/altsrc/yaml_file_loader.go
@@ -33,8 +33,12 @@ func NewYamlSourceFromFile(file string) (InputSourceContext, error) {
 // NewYamlSourceFromFlagFunc creates a new Yaml InputSourceContext from a provided flag name and source context.
 func NewYamlSourceFromFlagFunc(flagFileName string) func(context *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
-		filePath := context.String(flagFileName)
-		return NewYamlSourceFromFile(filePath)
+		if context.IsSet(flagFileName) {
+			filePath := context.String(flagFileName)
+			return NewYamlSourceFromFile(filePath)
+		}
+
+		return defaultInputSource()
 	}
 }