diff --git a/src/main.cpp b/src/main.cpp
index 5d32b51898..1e2a43871f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -329,6 +329,12 @@ int main(int argc, const char* argv[]) {
         /// just visit the ast
         AstVisitor().visit_program(*ast);
 
+        /// construct symbol table
+        {
+            logger->info("Running symtab visitor");
+            SymtabVisitor(update_symtab).visit_program(*ast);
+        }
+
         /// Check some rules that ast should follow
         {
             logger->info("Running semantic analysis visitor");
@@ -337,12 +343,6 @@ int main(int argc, const char* argv[]) {
             }
         }
 
-        /// construct symbol table
-        {
-            logger->info("Running symtab visitor");
-            SymtabVisitor(update_symtab).visit_program(*ast);
-        }
-
         /// use cnexp instead of after_cvode solve method
         {
             logger->info("Running CVode to cnexp visitor");
diff --git a/src/visitors/semantic_analysis_visitor.cpp b/src/visitors/semantic_analysis_visitor.cpp
index 618200edc3..602b2eb502 100644
--- a/src/visitors/semantic_analysis_visitor.cpp
+++ b/src/visitors/semantic_analysis_visitor.cpp
@@ -4,6 +4,7 @@
 #include "ast/program.hpp"
 #include "ast/suffix.hpp"
 #include "ast/table_statement.hpp"
+#include "symtab/symbol_properties.hpp"
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
@@ -22,6 +23,28 @@ bool SemanticAnalysisVisitor::check(const ast::Program& node) {
     }
     /// -->
 
+    /// <-- This code is for check 4
+    using namespace symtab::syminfo;
+    const auto& with_prop = NmodlType::read_ion_var | NmodlType::write_ion_var;
+
+    const auto& sym_table = node.get_symbol_table();
+    assert(sym_table != nullptr);
+
+    // get all ion variables
+    const auto& ion_variables = sym_table->get_variables_with_properties(with_prop, false);
+
+    /// make sure ion variables aren't redefined in a `CONSTANT` block.
+    for (const auto& var: ion_variables) {
+        if (var->has_any_property(NmodlType::constant_var)) {
+            logger->critical(
+                fmt::format("SemanticAnalysisVisitor :: ion variable {} from the USEION statement "
+                            "can not be re-declared in a CONSTANT block",
+                            var->get_name()));
+            check_fail = true;
+        }
+    }
+    /// -->
+
     visit_program(node);
     return check_fail;
 }
diff --git a/src/visitors/semantic_analysis_visitor.hpp b/src/visitors/semantic_analysis_visitor.hpp
index 7d1bbb90e2..35fef8d44b 100644
--- a/src/visitors/semantic_analysis_visitor.hpp
+++ b/src/visitors/semantic_analysis_visitor.hpp
@@ -25,8 +25,9 @@
  *
  * 1. Check that a function or a procedure containing a TABLE statement contains only one argument
  * (mandatory in mod2c).
- * 2. Check that destructor blocks are only inside mod file that are point_process
- * 3. A TABLE statement in functions cannot have name list, and should have one in procedures
+ * 2. Check that destructor blocks are only inside mod file that are point_process.
+ * 3. A TABLE statement in functions cannot have name list, and should have one in procedures.
+ * 4. Check if ion variables from a `USEION` statement are not declared in `CONSTANT` block.
  */
 #include "ast/ast.hpp"
 #include "visitors/ast_visitor.hpp"
diff --git a/test/unit/visitor/semantic_analysis.cpp b/test/unit/visitor/semantic_analysis.cpp
index 710cf35224..2e2314c1de 100644
--- a/test/unit/visitor/semantic_analysis.cpp
+++ b/test/unit/visitor/semantic_analysis.cpp
@@ -11,6 +11,7 @@
 #include "parser/nmodl_driver.hpp"
 #include "test/unit/utils/test_utils.hpp"
 #include "visitors/semantic_analysis_visitor.hpp"
+#include "visitors/symtab_visitor.hpp"
 
 
 using namespace nmodl;
@@ -26,6 +27,7 @@ using nmodl::parser::NmodlDriver;
 bool run_semantic_analysis_visitor(const std::string& text) {
     NmodlDriver driver;
     const auto& ast = driver.parse_string(text);
+    SymtabVisitor().visit_program(*ast);
     return SemanticAnalysisVisitor{}.check(*ast);
 }
 
@@ -105,3 +107,18 @@ SCENARIO("Destructor block", "[visitor][semantic_analysis]") {
         }
     }
 }
+
+SCENARIO("Ion variable in CONSTANT block", "[visitor][semantic_analysis]") {
+    GIVEN("A mod file with ion variable redeclared in a CONSTANT block") {
+        std::string nmodl_text = R"(
+            NEURON {
+                SUFFIX cdp4Nsp
+                USEION ca READ cao, cai, ica WRITE cai
+            }
+            CONSTANT { cao = 2  (mM) }
+        )";
+        THEN("Semantic analysis fails") {
+            REQUIRE(run_semantic_analysis_visitor(nmodl_text));
+        }
+    }
+}