diff --git a/api/optimize.py b/api/optimize.py
index e361fa9a0..c1f76cefa 100644
--- a/api/optimize.py
+++ b/api/optimize.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
+from typing import NamedTuple
 from ast_ import NodeVisitor
 from .config import OPTIONS
 import api.errmsg
@@ -24,28 +25,8 @@ def __init__(self, obj):
         self.obj = obj
 
 
-class OptimizerVisitor(NodeVisitor):
-    """ Implements some optimizations
-    """
-    NOP = symbols.NOP()  # Return this for "erased" nodes
-
-    @staticmethod
-    def TYPE(type_):
-        """ Converts a backend type (from api.constants)
-        to a SymbolTYPE object (taken from the SYMBOL_TABLE).
-        If type_ is already a SymbolTYPE object, nothing
-        is done.
-        """
-        if isinstance(type_, symbols.TYPE):
-            return type_
-
-        assert TYPE.is_valid(type_)
-        return gl.SYMBOL_TABLE.basic_types[type_]
-
+class GenericVisitor(NodeVisitor):
     def visit(self, node):
-        if self.O_LEVEL < 1:  # Optimize only if O1 or above
-            return node
-
         stack = [ToVisit(node)]
         last_result = None
 
@@ -76,6 +57,31 @@ def _visit(self, node):
 
         return meth(node.obj)
 
+
+class OptimizerVisitor(GenericVisitor):
+    """ Implements some optimizations
+    """
+    NOP = symbols.NOP()  # Return this for "erased" nodes
+
+    @staticmethod
+    def TYPE(type_):
+        """ Converts a backend type (from api.constants)
+        to a SymbolTYPE object (taken from the SYMBOL_TABLE).
+        If type_ is already a SymbolTYPE object, nothing
+        is done.
+        """
+        if isinstance(type_, symbols.TYPE):
+            return type_
+
+        assert TYPE.is_valid(type_)
+        return gl.SYMBOL_TABLE.basic_types[type_]
+
+    def visit(self, node):
+        if self.O_LEVEL < 1:  # Optimize only if O1 or above
+            return node
+
+        return super().visit(node)
+
     @property
     def O_LEVEL(self):
         return OPTIONS.optimization.value
@@ -196,7 +202,7 @@ def visit_IF(self, node):
             if not block_accessed and chk.is_number(expr_):  # constant condition
                 if expr_.value:  # always true (then_)
                     yield then_
-                else:            # always false (else_)
+                else:  # always false (else_)
                     yield else_
                 return
 
@@ -282,3 +288,70 @@ def _update_bound_status(self, arg: symbols.VARARRAY):
 
             if arg.scope == SCOPE.local and not arg.byref:
                 arg.scopeRef.owner.locals_size = api.symboltable.SymbolTable.compute_offsets(arg.scopeRef)
+
+
+class VarDependency(NamedTuple):
+    parent: symbols.VAR
+    dependency: symbols.VAR
+
+
+class VariableVisitor(GenericVisitor):
+    _original_variable = None
+    _parent_variable = None
+    _visited = set()
+
+    @staticmethod
+    def generic_visit(node):
+        if node not in VariableVisitor._visited:
+            VariableVisitor._visited.add(node)
+            for i in range(len(node.children)):
+                node.children[i] = yield ToVisit(node.children[i])
+            yield node
+
+    def has_circular_dependency(self, var_dependency: VarDependency) -> bool:
+        if var_dependency.dependency == VariableVisitor._original_variable:
+            api.errmsg.error(VariableVisitor._original_variable.lineno,
+                             "Circular dependency between '{}' and '{}'".format(
+                                 VariableVisitor._original_variable.name, var_dependency.parent))
+            return True
+
+        return False
+
+    def get_var_dependencies(self, var_entry: symbols.VAR):
+        visited = set()
+        result = set()
+
+        def visit_var(entry):
+            if entry in visited:
+                return
+
+            visited.add(entry)
+            if not isinstance(entry, symbols.VAR):
+                for child in entry.children:
+                    visit_var(child)
+                    if isinstance(child, symbols.VAR):
+                        result.add(VarDependency(parent=VariableVisitor._parent_variable, dependency=child))
+                return
+
+            VariableVisitor._parent_variable = entry
+            if entry.alias is not None:
+                result.add(VarDependency(parent=entry, dependency=entry.alias))
+                visit_var(entry.alias)
+            elif entry.addr is not None:
+                visit_var(entry.addr)
+
+        visit_var(var_entry)
+        return result
+
+    def visit_VARDECL(self, node: symbols.VARDECL):
+        """ Checks for cyclic dependencies in aliasing variables
+        """
+        VariableVisitor._visited = set()
+        VariableVisitor._original_variable = node.entry
+        for dependency in self.get_var_dependencies(node.entry):
+            if self.has_circular_dependency(dependency):
+                break
+
+        VariableVisitor._visited = set()
+        VariableVisitor._original_variable = VariableVisitor._parent_variable = None
+        yield node
diff --git a/libzxbc/zxb.py b/libzxbc/zxb.py
index f3aa528e3..39bff4556 100755
--- a/libzxbc/zxb.py
+++ b/libzxbc/zxb.py
@@ -331,6 +331,8 @@ def main(args=None, emitter=None):
     backend.MEMORY[:] = []
 
     # This will fill MEMORY with global declared variables
+    var_checker = api.optimize.VariableVisitor()
+    var_checker.visit(zxbparser.data_ast)
     translator = arch.zx48k.VarTranslator()
     translator.visit(zxbparser.data_ast)
     if gl.has_errors:
diff --git a/libzxbc/zxbparser.py b/libzxbc/zxbparser.py
index 3696dca36..bb7ea3b2f 100755
--- a/libzxbc/zxbparser.py
+++ b/libzxbc/zxbparser.py
@@ -669,7 +669,7 @@ def p_var_decl_at(p):
     if entry is None:
         return
 
-    if p[5].token == 'CONST':
+    if p[5].token in 'CONST':
         tmp = p[5].expr
         if tmp.token == 'UNARY' and tmp.operator == 'ADDRESS':  # Must be an ID
             if tmp.operand.token in ('VAR', 'LABEL'):
@@ -691,7 +691,7 @@ def p_var_decl_at(p):
         api.errmsg.syntax_error_address_must_be_constant(p.lineno(4))
         return
     else:
-        entry.addr = str(make_typecast(_TYPE(gl.PTR_TYPE), p[5], p.lineno(4)).value)
+        entry.addr = make_typecast(_TYPE(gl.PTR_TYPE), p[5], p.lineno(4))
         entry.accessed = True
         if entry.scope == SCOPE.local:
             SYMBOL_TABLE.make_static(entry.name)
diff --git a/tests/functional/dim_at_label4.bas b/tests/functional/dim_at_label4.bas
new file mode 100644
index 000000000..e80a5e22d
--- /dev/null
+++ b/tests/functional/dim_at_label4.bas
@@ -0,0 +1,7 @@
+REM Error: circular dependency
+
+DIM a at @b
+DIM b at @c
+DIM c at @a
+
+
diff --git a/tests/functional/dim_at_label5.bas b/tests/functional/dim_at_label5.bas
new file mode 100644
index 000000000..0c75e71a8
--- /dev/null
+++ b/tests/functional/dim_at_label5.bas
@@ -0,0 +1,4 @@
+REM Error: circular dependency
+
+DIM x at @x
+
diff --git a/tests/functional/dim_at_label6.bas b/tests/functional/dim_at_label6.bas
new file mode 100644
index 000000000..bfb859298
--- /dev/null
+++ b/tests/functional/dim_at_label6.bas
@@ -0,0 +1,4 @@
+
+DIM a at @b + 1
+DIM b at @c
+DIM c at @a
diff --git a/tests/functional/dim_at_label7.bas b/tests/functional/dim_at_label7.bas
new file mode 100644
index 000000000..bfb859298
--- /dev/null
+++ b/tests/functional/dim_at_label7.bas
@@ -0,0 +1,4 @@
+
+DIM a at @b + 1
+DIM b at @c
+DIM c at @a