diff --git a/core/src/main/java/org/lflang/generator/c/CParameterGenerator.java b/core/src/main/java/org/lflang/generator/c/CParameterGenerator.java
index 273f058d57..bcf03ea33a 100644
--- a/core/src/main/java/org/lflang/generator/c/CParameterGenerator.java
+++ b/core/src/main/java/org/lflang/generator/c/CParameterGenerator.java
@@ -1,5 +1,6 @@
 package org.lflang.generator.c;
 
+import java.util.HashSet;
 import org.lflang.ast.ASTUtils;
 import org.lflang.generator.CodeBuilder;
 import org.lflang.generator.ParameterInstance;
@@ -41,7 +42,14 @@ public static String getInitializer(ParameterInstance p) {
   public static String generateDeclarations(
       TypeParameterizedReactor reactor, CTypes types, boolean suppressLineDirectives) {
     CodeBuilder code = new CodeBuilder();
+    // Allow derived classes to override base class parameter definitions.
+    // Assume that the validator has checked that types match.
+    var declared = new HashSet<String>();
     for (Parameter parameter : ASTUtils.allParameters(reactor.reactor())) {
+      // If the parameter name has been seen already, assume it is an override of the default value
+      // in a derived class.  The validator should check.
+      if (declared.contains(parameter.getName())) continue;
+      declared.add(parameter.getName());
       code.prSourceLineNumber(parameter, suppressLineDirectives);
       code.pr(
           types.getTargetType(reactor.resolveType(ASTUtils.getInferredType(parameter)))
diff --git a/test/C/src/ParameterOverride.lf b/test/C/src/ParameterOverride.lf
new file mode 100644
index 0000000000..b586281dee
--- /dev/null
+++ b/test/C/src/ParameterOverride.lf
@@ -0,0 +1,16 @@
+target C
+
+reactor A(x: int = 0) {
+  reaction(startup) {=
+    if (self->x != 1) {
+      lf_print_error_and_exit("x is %d. Should be 1.", self->x);
+    }
+  =}
+}
+
+reactor B(x: int = 1) extends A {
+}
+
+main reactor {
+  b = new B()
+}