diff --git a/README.md b/README.md
index e51be820..d5499d19 100644
--- a/README.md
+++ b/README.md
@@ -44,7 +44,7 @@ Visit the documentation at [topgrade-rs.github.io](https://topgrade-rs.github.io
 > **Warning**
 > Work in Progress
 
-## Customization
+## Configuration 
 
 See `config.example.toml` for an example configuration file.
 
@@ -55,6 +55,14 @@ The configuration should be placed in the following paths depending on the opera
 - **Windows** - `%APPDATA%/topgrade.toml`
 - **macOS** and **other Unix systems** - `${XDG_CONFIG_HOME:-~/.config}/topgrade.toml`
 
+### Custom Commands
+
+Custom commands can be defined in the config file which can be run before, during, or after the inbuilt commands, as required.
+By default, the custom commands are run using a new shell according to the `$SHELL` environment variable on unix (falls back to `sh`) or `pwsh` on windows (falls back to `powershell`).
+
+On unix, if you want to run your command using an interactive shell, for example to source your shell's rc files, you can add `-i` at the start of your custom command.
+But note that this requires the command to exit the shell correctly or else the shell will hang indefinitely.
+
 ## Remote Execution
 
 You can specify a key called `remote_topgrades` in the configuration file.
diff --git a/config.example.toml b/config.example.toml
index 4c6bff93..0530a50b 100644
--- a/config.example.toml
+++ b/config.example.toml
@@ -74,6 +74,7 @@
 # Custom commands
 [commands]
 #"Python Environment" = "~/dev/.env/bin/pip install -i https://pypi.python.org/simple -U --upgrade-strategy eager jupyter"
+#"Custom command using interactive shell (unix)" = "-i vim_upgrade"
 
 [brew]
 #greedy_cask = true
diff --git a/src/steps/generic.rs b/src/steps/generic.rs
index f096574f..cb2a87f6 100644
--- a/src/steps/generic.rs
+++ b/src/steps/generic.rs
@@ -505,7 +505,15 @@ pub fn run_myrepos_update(base_dirs: &BaseDirs, run_type: RunType) -> Result<()>
 
 pub fn run_custom_command(name: &str, command: &str, ctx: &ExecutionContext) -> Result<()> {
     print_separator(name);
-    ctx.run_type().execute(shell()).arg("-c").arg(command).status_checked()
+    let mut exec = ctx.run_type().execute(shell());
+    #[cfg(unix)]
+    let command = if let Some(command) = command.strip_prefix("-i ") {
+        exec.arg("-i");
+        command
+    } else {
+        command
+    };
+    exec.arg("-c").arg(command).status_checked()
 }
 
 pub fn run_composer_update(ctx: &ExecutionContext) -> Result<()> {