diff --git a/src/lexer/token_mapping.cpp b/src/lexer/token_mapping.cpp
index 6a1ce6b7bb..57ae4a0f6e 100644
--- a/src/lexer/token_mapping.cpp
+++ b/src/lexer/token_mapping.cpp
@@ -244,6 +244,31 @@ const static std::vector<std::string> extern_definitions = {"acos",
                                                             "tanh",
                                                             "threshold"};
 const static std::vector<std::string> need_nt = {"at_time"};
+const static std::vector<std::string> not_thread_safe = {"force",
+                                                         "deflate",
+                                                         "expfit",
+                                                         "derivs",
+                                                         "spline",
+                                                         "exprand",
+                                                         "gauss",
+                                                         "normrand",
+                                                         "poisrand",
+                                                         "poisson",
+                                                         "setseed",
+                                                         "scop_random",
+                                                         "boundary",
+                                                         "romberg",
+                                                         "invert",
+                                                         "stepforce",
+                                                         "schedule",
+                                                         "set_seed",
+                                                         "nrn_random_play"};
+
+bool is_external_definitions(const std::string& token) {
+    return std::find(extern_definitions.cbegin(), extern_definitions.cend(), token) !=
+           extern_definitions.cend();
+}
+
 
 /**
  * Checks if \c token is one of the functions coming from NEURON/CoreNEURON and needs
@@ -257,6 +282,12 @@ bool needs_neuron_thread_first_arg(const std::string& token) {
 }
 
 
+bool is_not_thread_safe(const std::string& token) {
+    return std::find(not_thread_safe.cbegin(), not_thread_safe.cend(), token) !=
+           not_thread_safe.cend();
+}
+
+
 /**
  * Variables from NEURON that are directly used in NMODL
  *
diff --git a/src/lexer/token_mapping.hpp b/src/lexer/token_mapping.hpp
index 6f1fb3255f..a39f9e4d3f 100644
--- a/src/lexer/token_mapping.hpp
+++ b/src/lexer/token_mapping.hpp
@@ -27,7 +27,9 @@ std::vector<std::string> get_external_functions();
 
 namespace details {
 
+bool is_external_definitions(const std::string& token);
 bool needs_neuron_thread_first_arg(const std::string& token);
+bool is_not_thread_safe(const std::string& token);
 
 }  // namespace details
 
diff --git a/src/visitors/semantic_analysis_visitor.cpp b/src/visitors/semantic_analysis_visitor.cpp
index 602b2eb502..107f9c4ed3 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 "lexer/token_mapping.hpp"
 #include "symtab/symbol_properties.hpp"
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
@@ -101,5 +102,17 @@ void SemanticAnalysisVisitor::visit_destructor_block(const ast::DestructorBlock&
     /// -->
 }
 
+void SemanticAnalysisVisitor::visit_function_call(const ast::FunctionCall& node) {
+    /// <-- This code is for check 5
+    const auto& name = node.get_node_name();
+    if (details::is_external_definitions(name) && details::is_not_thread_safe(name)) {
+        logger->critical(
+            "SemanticAnalysisVisitor :: '{}' is not thread safe and incompatible with CoreNEURON",
+            name);
+        check_fail = true;
+    }
+    /// -->
+}
+
 }  // namespace visitor
 }  // namespace nmodl
diff --git a/src/visitors/semantic_analysis_visitor.hpp b/src/visitors/semantic_analysis_visitor.hpp
index 35fef8d44b..09a78e0cd9 100644
--- a/src/visitors/semantic_analysis_visitor.hpp
+++ b/src/visitors/semantic_analysis_visitor.hpp
@@ -28,6 +28,7 @@
  * 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.
+ * 5. Check that an external definition is allowed by CoreNeuron
  */
 #include "ast/ast.hpp"
 #include "visitors/ast_visitor.hpp"
@@ -60,6 +61,10 @@ class SemanticAnalysisVisitor: public ConstAstVisitor {
     /// Visit destructor and check that the file is of type POINT_PROCESS or ARTIFICIAL_CELL
     void visit_destructor_block(const ast::DestructorBlock& node) override;
 
+    /// Visit function call and check if the function is not thread safe and so not
+    /// compatible with CoreNeuron
+    void visit_function_call(const ast::FunctionCall& node) override;
+
   public:
     SemanticAnalysisVisitor() = default;