diff --git a/pw_libc/BUILD.gn b/pw_libc/BUILD.gn
index 2ff58b11a7..9374463c87 100644
--- a/pw_libc/BUILD.gn
+++ b/pw_libc/BUILD.gn
@@ -53,7 +53,15 @@ config("no-shadow") {
 # pw_libc.a from llvm-libc. Otherwise, we create an empty pw_libc.a.
 if (dir_pw_third_party_llvm_libc != "") {
   pw_libc_source_set("stdlib") {
-    functions = [ "abs" ]
+    functions = [
+      "abs",
+      "rand",
+      "srand",
+    ]
+    additional_srcs = [ "rand_util.cpp" ]
+
+    # srand and rand are both tested in rand_test.cpp.
+    no_test_functions = [ "srand" ]
   }
 
   pw_libc_source_set("string") {
diff --git a/third_party/llvm_libc/llvm_libc.gni b/third_party/llvm_libc/llvm_libc.gni
index 05f80b052c..e9414408b9 100644
--- a/third_party/llvm_libc/llvm_libc.gni
+++ b/third_party/llvm_libc/llvm_libc.gni
@@ -31,6 +31,11 @@ template("pw_libc_source_set") {
   pw_source_set(target_name) {
     dir = target_dir
 
+    additional_srcs = []
+    if (defined(invoker.additional_srcs)) {
+      additional_srcs = invoker.additional_srcs
+    }
+
     include_dirs = [ dir_pw_third_party_llvm_libc ]
 
     defines = [
@@ -48,6 +53,7 @@ template("pw_libc_source_set") {
                              "defines",
                              "functions",
                              "no_test_functions",
+                             "additional_srcs",
                            ])
 
     public = []
@@ -57,6 +63,10 @@ template("pw_libc_source_set") {
       public += [ "$dir/$function.h" ]
       sources += [ "$dir/$function.cpp" ]
     }
+
+    foreach(src, additional_srcs) {
+      sources += [ "$dir/$src" ]
+    }
   }
 
   pw_test("${source_set_target_name}_tests") {
@@ -75,6 +85,7 @@ template("pw_libc_source_set") {
                              "defines",
                              "functions",
                              "no_test_functions",
+                             "additional_srcs",
                            ])
 
     sources = []