diff --git a/src/libexpr-c/nix_api_value.cc b/src/libexpr-c/nix_api_value.cc
index 0d61292c4..0366e5020 100644
--- a/src/libexpr-c/nix_api_value.cc
+++ b/src/libexpr-c/nix_api_value.cc
@@ -513,7 +513,7 @@ nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * p)
     NIXC_CATCH_ERRS
 }
 
-nix_err nix_copy_value(nix_c_context * context, Value * value, Value * source)
+nix_err nix_copy_value(nix_c_context * context, Value * value, const Value * source)
 {
     if (context)
         context->last_err_code = NIX_OK;
diff --git a/src/libexpr-c/nix_api_value.h b/src/libexpr-c/nix_api_value.h
index d8bd77c33..b2b3439ef 100644
--- a/src/libexpr-c/nix_api_value.h
+++ b/src/libexpr-c/nix_api_value.h
@@ -422,7 +422,7 @@ nix_err nix_init_primop(nix_c_context * context, Value * value, PrimOp * op);
  * @param[in] source value to copy from
  * @return error code, NIX_OK on success.
  */
-nix_err nix_copy_value(nix_c_context * context, Value * value, Value * source);
+nix_err nix_copy_value(nix_c_context * context, Value * value, const Value * source);
 /**@}*/
 
 /** @brief Create a bindings builder
diff --git a/tests/unit/libexpr/nix_api_value.cc b/tests/unit/libexpr/nix_api_value.cc
index 6e209695e..6e1131e10 100644
--- a/tests/unit/libexpr/nix_api_value.cc
+++ b/tests/unit/libexpr/nix_api_value.cc
@@ -367,4 +367,17 @@ TEST_F(nix_api_expr_test, nix_value_init_apply_lazy_arg)
     nix_gc_decref(ctx, e);
 }
 
+TEST_F(nix_api_expr_test, nix_copy_value)
+{
+    Value * source = nix_alloc_value(ctx, state);
+
+    nix_init_int(ctx, source, 42);
+    nix_copy_value(ctx, value, source);
+
+    ASSERT_EQ(42, nix_get_int(ctx, value));
+
+    // Clean up
+    nix_gc_decref(ctx, source);
+}
+
 }