diff --git a/yara-x/src/compiler/context.rs b/yara-x/src/compiler/context.rs
index 14abe4f58..6aac69cf9 100644
--- a/yara-x/src/compiler/context.rs
+++ b/yara-x/src/compiler/context.rs
@@ -49,8 +49,8 @@ pub(in crate::compiler) struct Context<'a, 'src, 'sym> {
     /// Rule that is being compiled.
     pub current_rule: &'a RuleInfo,
 
-    // IR nodes for patterns defined in the rule being compiled.
-    pub current_rule_patterns: &'a mut Vec<ir::Pattern<'src>>,
+    /// IR nodes for patterns defined in the rule being compiled.
+    pub current_rule_patterns: &'a mut FxHashMap<PatternId, ir::Pattern<'src>>,
 
     /// Warnings generated during the compilation.
     pub warnings: &'a mut Vec<Warning>,
@@ -82,16 +82,6 @@ pub(in crate::compiler) struct Context<'a, 'src, 'sym> {
 }
 
 impl<'a, 'src, 'sym> Context<'a, 'src, 'sym> {
-    /// Given an [`IdentId`] returns the identifier as `&str`.
-    ///
-    /// # Panics
-    ///
-    /// Panics if no identifier has the provided [`IdentId`].
-    #[inline]
-    pub fn resolve_ident(&self, ident_id: IdentId) -> &str {
-        self.ident_pool.get(ident_id).unwrap()
-    }
-
     /// Returns a [`RuleInfo`] given its [`RuleId`].
     ///
     /// # Panics
@@ -120,19 +110,15 @@ impl<'a, 'src, 'sym> Context<'a, 'src, 'sym> {
                 .expect("identifier must be at least 1 character long")
         ));
 
-        for (ident_id, pattern_id) in &self.current_rule.patterns {
+        for (pattern_id, pattern) in self.current_rule_patterns.iter() {
             // Ignore the first character (`$`, `#`, `@` or `!`) while
             // comparing the identifiers.
-            if self.resolve_ident(*ident_id)[1..] == ident[1..] {
+            if pattern.identifier()[1..] == ident[1..] {
                 return *pattern_id;
             }
         }
 
-        panic!(
-            "rule `{}` does not have pattern `{}` ",
-            self.resolve_ident(self.current_rule.ident_id),
-            ident
-        );
+        panic!("pattern `{}` not found", ident);
     }
 
     /// Given a pattern identifier (e.g. `$a`, `#a`, `@a`) search for it in
@@ -154,11 +140,12 @@ impl<'a, 'src, 'sym> Context<'a, 'src, 'sym> {
                 .expect("identifier must be at least 1 character long")
         ));
 
-        for p in self.current_rule_patterns.iter_mut() {
-            if p.identifier()[1..] == ident[1..] {
-                return p;
+        for (_, pattern) in self.current_rule_patterns.iter_mut() {
+            if pattern.identifier()[1..] == ident[1..] {
+                return pattern;
             }
         }
+
         panic!("pattern `{}` not found", ident);
     }
 
diff --git a/yara-x/src/compiler/ir/ast2ir.rs b/yara-x/src/compiler/ir/ast2ir.rs
index 78b20d03d..46d2983d3 100644
--- a/yara-x/src/compiler/ir/ast2ir.rs
+++ b/yara-x/src/compiler/ir/ast2ir.rs
@@ -617,8 +617,8 @@ fn of_expr_from_ast(
         // `x of them`, `x of ($a*, $b)`
         ast::OfItems::PatternSet(pattern_set) => {
             let pattern_ids = pattern_set_from_ast(ctx, pattern_set);
-            let num_items = pattern_ids.len();
-            (OfItems::PatternSet(pattern_ids), num_items)
+            let num_patterns = pattern_ids.len();
+            (OfItems::PatternSet(pattern_ids), num_patterns)
         }
     };
 
@@ -1030,28 +1030,36 @@ fn pattern_set_from_ast(
     ctx: &mut Context,
     pattern_set: &ast::PatternSet,
 ) -> Vec<PatternId> {
-    match pattern_set {
+    let pattern_ids = match pattern_set {
         // `x of them`
         ast::PatternSet::Them => ctx
-            .current_rule
-            .patterns
+            .current_rule_patterns
             .iter()
-            .map(|(_, pattern_id)| *pattern_id)
+            .map(|(pattern_id, _)| *pattern_id)
             .collect(),
         // `x of ($a*, $b)`
-        ast::PatternSet::Set(ref set_patterns) => {
+        ast::PatternSet::Set(ref set) => {
             let mut pattern_ids = Vec::new();
-            for (ident_id, pattern_id) in &ctx.current_rule.patterns {
-                let ident = ctx.resolve_ident(*ident_id);
+            for (pattern_id, pattern) in ctx.current_rule_patterns.iter() {
                 // Iterate over the patterns in the set (e.g: $foo, $foo*) and
                 // check if some of them matches the identifier.
-                if set_patterns.iter().any(|p| p.matches(ident)) {
+                if set.iter().any(|p| p.matches(pattern.identifier())) {
                     pattern_ids.push(*pattern_id);
                 }
             }
             pattern_ids
         }
+    };
+
+    // Make all the patterns in the set non-anchorable.
+    for pattern_id in pattern_ids.iter() {
+        ctx.current_rule_patterns
+            .get_mut(pattern_id)
+            .unwrap()
+            .make_non_anchorable();
     }
+
+    pattern_ids
 }
 
 fn func_call_from_ast(
diff --git a/yara-x/src/compiler/mod.rs b/yara-x/src/compiler/mod.rs
index 4a87f84e4..6d5931837 100644
--- a/yara-x/src/compiler/mod.rs
+++ b/yara-x/src/compiler/mod.rs
@@ -559,24 +559,29 @@ impl<'a> Compiler<'a> {
         self.check_for_existing_identifier(&rule.identifier)?;
 
         // Convert the patterns from AST to IR.
-        let mut patterns =
+        let patterns =
             patterns_from_ast(&self.report_builder, rule.patterns.as_ref())?;
 
         let num_patterns: usize = patterns.len();
 
-        // Create array with pairs (IdentId, PatternId) that describe
-        // the patterns in a compiled rule.
-        let mut ident_and_pattern = Vec::with_capacity(num_patterns);
+        // Create array with pairs (IdentId, PatternId)
+        let mut ident_and_pattern_ids = Vec::with_capacity(num_patterns);
+
+        // Create a map (IdentId, Pattern).
+        let mut patterns_map: FxHashMap<PatternId, Pattern> =
+            FxHashMap::default();
 
         for (pattern_id, pattern) in
-            iter::zip(self.next_pattern_id.successors(), &patterns)
+            iter::zip(self.next_pattern_id.successors(), patterns)
         {
             // Save pattern identifier (e.g: $a) in the pool of identifiers
             // or reuse the IdentId if the identifier has been used already.
-            ident_and_pattern.push((
+            ident_and_pattern_ids.push((
                 self.ident_pool.get_or_intern(pattern.identifier()),
                 pattern_id,
             ));
+
+            patterns_map.insert(pattern_id, pattern);
         }
 
         let rule_id = RuleId(self.rules.len() as i32);
@@ -586,7 +591,7 @@ impl<'a> Compiler<'a> {
             namespace_ident_id: self.current_namespace.ident_id,
             ident_id: self.ident_pool.get_or_intern(rule.identifier.name),
             ident_span: rule.identifier.span,
-            patterns: ident_and_pattern,
+            patterns: ident_and_pattern_ids,
             is_global: rule.flags.contains(RuleFlag::Global),
             is_private: rule.flags.contains(RuleFlag::Private),
         });
@@ -619,7 +624,7 @@ impl<'a> Compiler<'a> {
             report_builder: &self.report_builder,
             rules: &self.rules,
             current_rule: self.rules.last().unwrap(),
-            current_rule_patterns: &mut patterns,
+            current_rule_patterns: &mut patterns_map,
             wasm_symbols: &self.wasm_symbols,
             wasm_exports: &self.wasm_exports,
             warnings: &mut self.warnings,
@@ -647,13 +652,12 @@ impl<'a> Compiler<'a> {
 
         drop(ctx);
 
-        let patterns_with_span = itertools::multizip((
-            self.next_pattern_id.successors(),
-            patterns,
+        let patterns_with_span = iter::zip(
+            patterns_map,
             rule.patterns.iter().flatten().map(|p| p.span()),
-        ));
+        );
 
-        for (pattern_id, pattern, span) in patterns_with_span {
+        for ((pattern_id, pattern), span) in patterns_with_span {
             self.current_pattern_id = pattern_id;
             match pattern {
                 Pattern::Literal(pattern) => {
diff --git a/yara-x/src/tests/mod.rs b/yara-x/src/tests/mod.rs
index 574273afd..acade487c 100644
--- a/yara-x/src/tests/mod.rs
+++ b/yara-x/src/tests/mod.rs
@@ -1134,6 +1134,19 @@ fn match_at() {
         b"foobar"
     );
 
+    rule_true!(
+        r#"
+        rule test {
+            strings: 
+                $a = "foo" 
+                $b = "bar"
+            condition: 
+                2 of ($a, $b) or $b at 0
+        }
+        "#,
+        b"foobar"
+    );
+
     rule_false!(
         r#"
         rule test {