diff --git a/src/display_node.rs b/src/display_node.rs
index 7f1f6276..9a4bcbcf 100644
--- a/src/display_node.rs
+++ b/src/display_node.rs
@@ -1,8 +1,12 @@
+use std::cell::RefCell;
 use std::path::PathBuf;
 
-use serde::Serialize;
+use serde::ser::SerializeStruct;
+use serde::{Serialize, Serializer};
 
-#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone, Serialize)]
+use crate::display::human_readable_number;
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
 pub struct DisplayNode {
     // Note: the order of fields in important here, for PartialEq and PartialOrd
     pub size: u64,
@@ -25,3 +29,30 @@ impl DisplayNode {
         out
     }
 }
+
+// Only used for -j 'json' flag combined with -o 'output_type' flag
+// Used to pass the output_type into the custom Serde serializer
+thread_local! {
+    pub static OUTPUT_TYPE: RefCell<String> = const { RefCell::new(String::new()) };
+}
+
+/*
+We need the custom Serialize incase someone uses the -o flag to pass a custom output type in
+(show size in Mb / Gb etc).
+Sadly this also necessitates a global variable OUTPUT_TYPE as we can not pass the output_type flag
+into the serialize method
+ */
+impl Serialize for DisplayNode {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let readable_size = OUTPUT_TYPE
+            .with(|output_type| human_readable_number(self.size, output_type.borrow().as_str()));
+        let mut state = serializer.serialize_struct("DisplayNode", 2)?;
+        state.serialize_field("size", &(readable_size))?;
+        state.serialize_field("name", &self.name)?;
+        state.serialize_field("children", &self.children)?;
+        state.end()
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index ddc50ee1..823459ea 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -33,6 +33,7 @@ use sysinfo::{System, SystemExt};
 use self::display::draw_it;
 use config::get_config;
 use dir_walker::walk_it;
+use display_node::OUTPUT_TYPE;
 use filter::get_biggest;
 use filter_type::get_all_file_types;
 use regex::Regex;
@@ -327,20 +328,24 @@ fn main() {
     }
 
     if let Some(root_node) = tree {
-        let idd = InitialDisplayData {
-            short_paths: !config.get_full_paths(&options),
-            is_reversed: !config.get_reverse(&options),
-            colors_on: is_colors,
-            by_filecount,
-            by_filetime,
-            is_screen_reader: config.get_screen_reader(&options),
-            output_format,
-            bars_on_right: config.get_bars_on_right(&options),
-        };
-
         if config.get_output_json(&options) {
+            OUTPUT_TYPE.with(|wrapped| {
+                wrapped.replace(output_format);
+            });
             println!("{}", serde_json::to_string(&root_node).unwrap());
         } else {
+            let idd = InitialDisplayData {
+                short_paths: !config.get_full_paths(&options),
+                is_reversed: !config.get_reverse(&options),
+                colors_on: is_colors,
+                by_filecount,
+                by_filetime,
+                is_screen_reader: config.get_screen_reader(&options),
+                output_format,
+                bars_on_right: config.get_bars_on_right(&options),
+            };
+
+
             draw_it(
                 idd,
                 config.get_no_bars(&options),