diff --git a/core/src/main/java/org/lflang/generator/c/CGenerator.java b/core/src/main/java/org/lflang/generator/c/CGenerator.java
index 4d77463c4f..567b04ba4f 100644
--- a/core/src/main/java/org/lflang/generator/c/CGenerator.java
+++ b/core/src/main/java/org/lflang/generator/c/CGenerator.java
@@ -973,6 +973,7 @@ protected void generateReactorClassHeaders(
     }
     header.pr("#include \"include/core/reactor.h\"");
     src.pr("#include \"include/api/api.h\"");
+    src.pr("#include \"include/core/platform.h\"");
     generateIncludes(tpr);
     if (cppMode) {
       src.pr("}");
diff --git a/core/src/main/java/org/lflang/generator/c/CReactionGenerator.java b/core/src/main/java/org/lflang/generator/c/CReactionGenerator.java
index b5db35ce92..e1123e8312 100644
--- a/core/src/main/java/org/lflang/generator/c/CReactionGenerator.java
+++ b/core/src/main/java/org/lflang/generator/c/CReactionGenerator.java
@@ -336,6 +336,7 @@ public static String generateForwardBody(
         ? String.join(
             "\n",
             DISABLE_REACTION_INITIALIZATION_MARKER,
+            "lf_critical_section_enter(self->base.environment);",
             "self->_lf_"
                 + outputName
                 + ".value = ("
@@ -348,7 +349,8 @@ public static String generateForwardBody(
                 + ", (lf_token_t*)self->_lf__"
                 + actionName
                 + ".tmplt.token);",
-            "self->_lf_" + outputName + ".is_present = true;")
+            "self->_lf_" + outputName + ".is_present = true;",
+            "lf_critical_section_exit(self->base.environment);")
         : "lf_set(" + outputName + ", " + actionName + "->value);";
   }
 
@@ -551,6 +553,7 @@ private static String generateActionVariablesInReaction(
     builder.pr(
         String.join(
             "\n",
+            "lf_critical_section_enter(self->base.environment);",
             "// Expose the action struct as a local variable whose name matches the action name.",
             structType + "* " + action.getName() + " = &self->_lf_" + action.getName() + ";",
             "// Set the fields of the action struct to match the current trigger.",
@@ -565,7 +568,8 @@ private static String generateActionVariablesInReaction(
                 + action.getName()
                 + ", "
                 + tokenPointer
-                + ");"));
+                + ");",
+            "lf_critical_section_exit(self->base.environment);"));
     // Set the value field only if there is a type.
     if (!type.isUndefined()) {
       // The value field will either be a copy (for primitive types)