diff --git a/src-tauri/yaak-templates/src/error.rs b/src-tauri/yaak-templates/src/error.rs
index c1df0377..e093f9c2 100644
--- a/src-tauri/yaak-templates/src/error.rs
+++ b/src-tauri/yaak-templates/src/error.rs
@@ -6,6 +6,9 @@ pub enum Error {
     #[error("Render Error: {0}")]
     RenderError(String),
 
+    #[error("Render Error: Variable \"{0}\" is not defined in active environment")]
+    VariableNotFound(String),
+
     #[error("Render Error: Max recursion depth exceeded")]
     RenderStackExceededError,
 }
diff --git a/src-tauri/yaak-templates/src/parser.rs b/src-tauri/yaak-templates/src/parser.rs
index 30470d16..f4d6791c 100644
--- a/src-tauri/yaak-templates/src/parser.rs
+++ b/src-tauri/yaak-templates/src/parser.rs
@@ -269,9 +269,9 @@ impl Parser {
         while self.pos < self.chars.len() {
             let ch = self.peek_char();
             let is_valid = if start_pos == self.pos {
-                ch.is_alphabetic() // First char has to be alphabetic
+                ch.is_alphabetic() || ch == '_' // First is more restrictive
             } else {
-                ch.is_alphanumeric() || ch == '-' || ch == '_'
+                ch.is_alphanumeric() || ch == '_' || ch == '-'
             };
             if is_valid {
                 text.push(ch);
@@ -457,13 +457,13 @@ mod tests {
 
     #[test]
     fn var_prefixes() {
-        let mut p = Parser::new("${[ -a ]}${[ _a ]}${[ 0a ]}");
+        let mut p = Parser::new("${[ -a ]}${[ 0a ]}");
         assert_eq!(
             p.parse().tokens,
             vec![
                 Token::Raw {
                     // Shouldn't be parsed, because they're invalid
-                    text: "${[ -a ]}${[ _a ]}${[ 0a ]}".into()
+                    text: "${[ -a ]}${[ 0a ]}".into()
                 },
                 Token::Eof
             ]
@@ -476,8 +476,8 @@ mod tests {
         assert_eq!(
             p.parse().tokens,
             vec![
-                Token::Raw {
-                    text: "${[ _a ]}".into()
+                Token::Tag {
+                    val: Val::Var { name: "_a".into() }
                 },
                 Token::Eof
             ]
diff --git a/src-tauri/yaak-templates/src/renderer.rs b/src-tauri/yaak-templates/src/renderer.rs
index b87b76d4..a9e378a3 100644
--- a/src-tauri/yaak-templates/src/renderer.rs
+++ b/src-tauri/yaak-templates/src/renderer.rs
@@ -1,4 +1,4 @@
-use crate::error::Error::RenderStackExceededError;
+use crate::error::Error::{RenderStackExceededError, VariableNotFound};
 use crate::error::Result;
 use crate::{FnArg, Parser, Token, Tokens, Val};
 use log::warn;
@@ -100,7 +100,7 @@ async fn render_tag<T: TemplateCallback>(
                 let r = Box::pin(parse_and_render_with_depth(v, vars, cb, depth)).await?;
                 r.to_string()
             }
-            None => "".into(),
+            None => return Err(VariableNotFound(name)),
         },
         Val::Bool { value } => value.to_string(),
         Val::Fn { name, args } => {
@@ -142,7 +142,7 @@ async fn render_tag<T: TemplateCallback>(
 
 #[cfg(test)]
 mod parse_and_render_tests {
-    use crate::error::Error::{RenderError, RenderStackExceededError};
+    use crate::error::Error::{RenderError, RenderStackExceededError, VariableNotFound};
     use crate::error::Result;
     use crate::renderer::TemplateCallback;
     use crate::*;
@@ -200,6 +200,19 @@ mod parse_and_render_tests {
         Ok(())
     }
 
+    #[tokio::test]
+    async fn render_missing_var() -> Result<()> {
+        let empty_cb = EmptyCB {};
+        let template = "${[ foo ]}";
+        let vars = HashMap::new();
+
+        assert_eq!(
+            parse_and_render(template, &vars, &empty_cb).await,
+            Err(VariableNotFound("foo".to_string()))
+        );
+        Ok(())
+    }
+
     #[tokio::test]
     async fn render_self_referencing_var() -> Result<()> {
         let empty_cb = EmptyCB {};
diff --git a/src-web/components/EnvironmentEditDialog.tsx b/src-web/components/EnvironmentEditDialog.tsx
index c84a97d8..589e43e2 100644
--- a/src-web/components/EnvironmentEditDialog.tsx
+++ b/src-web/components/EnvironmentEditDialog.tsx
@@ -160,7 +160,7 @@ const EnvironmentEditor = function ({
   const validateName = useCallback((name: string) => {
     // Empty just means the variable doesn't have a name yet, and is unusable
     if (name === '') return true;
-    return name.match(/^[a-z][a-z0-9_-]*$/i) != null;
+    return name.match(/^[a-z_][a-z0-9_-]*$/i) != null;
   }, []);
 
   return (