diff --git a/askama_derive/Cargo.toml b/askama_derive/Cargo.toml
index 4a676443..b1c3981f 100644
--- a/askama_derive/Cargo.toml
+++ b/askama_derive/Cargo.toml
@@ -25,7 +25,7 @@ with-rocket = []
 with-warp = []
 
 [dependencies]
-parser = { package = "askama_parser", version = "0.3", path = "../askama_parser" }
+parser = { package = "askama_parser", version = "0.3.1", path = "../askama_parser" }
 mime = "0.3"
 mime_guess = "2"
 proc-macro2 = "1"
diff --git a/askama_derive/src/config.rs b/askama_derive/src/config.rs
index 599d5a24..19358371 100644
--- a/askama_derive/src/config.rs
+++ b/askama_derive/src/config.rs
@@ -7,6 +7,7 @@ use std::{env, fs};
 use serde::Deserialize;
 
 use crate::{CompileError, CRATE};
+use parser::expr::TWO_PLUS_CHAR_OPS;
 use parser::node::Whitespace;
 use parser::Syntax;
 
@@ -147,20 +148,23 @@ impl<'a> TryInto<Syntax<'a>> for RawSyntax<'a> {
             comment_end: self.comment_end.unwrap_or(default.comment_end),
         };
 
-        for s in [
-            syntax.block_start,
-            syntax.block_end,
-            syntax.expr_start,
-            syntax.expr_end,
-            syntax.comment_start,
-            syntax.comment_end,
+        for (s, kind) in [
+            (syntax.block_start, "block_start"),
+            (syntax.block_end, "block_end"),
+            (syntax.expr_start, "expr_start"),
+            (syntax.expr_end, "expr_end"),
+            (syntax.comment_start, "comment_start"),
+            (syntax.comment_end, "comment_end"),
         ] {
             if s.len() < 2 {
-                return Err(
-                    format!("delimiters must be at least two characters long: {s:?}").into(),
-                );
+                return Err(format!(
+                    "{kind} delimiter must be at least two characters long: {s:?}"
+                )
+                .into());
             } else if s.chars().any(|c| c.is_whitespace()) {
-                return Err(format!("delimiters may not contain white spaces: {s:?}").into());
+                return Err(format!("{kind} delimiter may not contain whitespace: {s:?}").into());
+            } else if TWO_PLUS_CHAR_OPS.contains(&s) {
+                return Err(format!("{kind} delimiter may not contain operators: {s:?}").into());
             }
         }
 
@@ -486,7 +490,7 @@ mod tests {
         let config = Config::new(raw_config, None);
         assert_eq!(
             config.unwrap_err().msg,
-            r#"delimiters must be at least two characters long: "<""#,
+            r#"block_start delimiter must be at least two characters long: "<""#,
         );
 
         let raw_config = r#"
@@ -497,7 +501,7 @@ mod tests {
         let config = Config::new(raw_config, None);
         assert_eq!(
             config.unwrap_err().msg,
-            r#"delimiters may not contain white spaces: " {{ ""#,
+            r#"block_start delimiter may not contain whitespace: " {{ ""#,
         );
 
         let raw_config = r#"
diff --git a/askama_parser/Cargo.toml b/askama_parser/Cargo.toml
index 789a41fc..92727a91 100644
--- a/askama_parser/Cargo.toml
+++ b/askama_parser/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "askama_parser"
-version = "0.3.0"
+version = "0.3.1"
 description = "Parser for Askama templates"
 documentation = "https://docs.rs/askama"
 keywords = ["markup", "template", "jinja2", "html"]
diff --git a/askama_parser/src/expr.rs b/askama_parser/src/expr.rs
index 16069b2d..4ea4fe60 100644
--- a/askama_parser/src/expr.rs
+++ b/askama_parser/src/expr.rs
@@ -172,6 +172,7 @@ impl<'a> Expr<'a> {
         ))(i)
     }
 
+    // Keep in sync with `TWO_PLUS_CHAR_OPS`, below
     expr_prec_layer!(or, and, "||");
     expr_prec_layer!(and, compare, "&&");
     expr_prec_layer!(compare, bor, "==", "!=", ">=", ">", "<=", "<");
@@ -430,3 +431,6 @@ impl<'a> Suffix<'a> {
         map(preceded(take_till(not_ws), char('?')), |_| Self::Try)(i)
     }
 }
+
+pub const TWO_PLUS_CHAR_OPS: &[&str] =
+    &["||", "&&", "==", "!=", ">=", "<=", "<<", ">>", "..", "..="];