diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -1484,6 +1484,12 @@
   // Update various call graph maps.
   G->NodeMap.erase(&OldF);
   G->NodeMap[&NewF] = &N;
+
+  // Update lib functions.
+  if (G->isLibFunction(OldF)) {
+    G->LibFunctions.remove(&OldF);
+    G->LibFunctions.insert(&NewF);
+  }
 }
 
 void LazyCallGraph::insertEdge(Node &SourceN, Node &TargetN, Edge::Kind EK) {
diff --git a/llvm/test/Analysis/LazyCallGraph/replace-libcall.ll b/llvm/test/Analysis/LazyCallGraph/replace-libcall.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/LazyCallGraph/replace-libcall.ll
@@ -0,0 +1,17 @@
+; RUN: opt -passes=inline,argpromotion < %s -S | FileCheck %s
+
+; Make sure we update the list of libcalls when we replace a libcall.
+
+; CHECK: define {{.*}}@a
+
+define void @a() {
+entry:
+  %call = call float @strtof(ptr noundef null, ptr noundef null)
+  ret void
+}
+
+define internal float @strtof(ptr noundef %0, ptr noundef %1) nounwind {
+entry:
+  ret float 0.0
+}
+