diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -809,9 +809,17 @@
 }
 
 Symbol *SymbolTable::findMangle(StringRef name) {
-  if (Symbol *sym = find(name))
-    if (!isa<Undefined>(sym))
+  if (Symbol *sym = find(name)) {
+    if (auto *u = dyn_cast<Undefined>(sym)) {
+      // We're specifically looking for weak aliases that ultimately resolve to
+      // defined symbols, hence the call to getWeakAlias() instead of just using
+      // the weakAlias member variable. This matches link.exe's behavior.
+      if (Symbol *weakAlias = u->getWeakAlias())
+        return weakAlias;
+    } else {
       return sym;
+    }
+  }
 
   // Efficient fuzzy string lookup is impossible with a hash table, so iterate
   // the symbol table once and collect all possibly matching symbols into this
diff --git a/lld/test/COFF/entry-weak-external.s b/lld/test/COFF/entry-weak-external.s
new file mode 100644
--- /dev/null
+++ b/lld/test/COFF/entry-weak-external.s
@@ -0,0 +1,41 @@
+# REQUIRES: x86
+# RUN: rm -rf %t && split-file %s %t
+
+## Ensure that we resolve the entry point to the unmangled weak alias instead of
+## the mangled library definition (which would fail with an undefined symbol).
+
+# RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t/entry-weak.obj %t/entry-weak.s
+# RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t/entry-mangled.obj %t/entry-mangled.s
+# RUN: llvm-lib -out:%t/entry-mangled.lib %t/entry-mangled.obj
+# RUN: lld-link -subsystem:console -entry:entry -out:%t/entry-weak-external.exe %t/entry-weak.obj %t/entry-mangled.lib
+# RUN: llvm-readobj --file-headers %t/entry-weak-external.exe | FileCheck %s
+
+## Ensure that we don't resolve the entry point to a weak alias pointing to an
+## undefined symbol (which would have caused the entry point to be 0 instead of
+## an actual address). I can't think of a way of triggering this edge case
+## without using /force:unresolved, which means it likely doesn't matter in
+## practice, but we still match link.exe's behavior for it.
+
+# RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t/entry-weak-undefined.obj %t/entry-weak-undefined.s
+# RUN: lld-link -subsystem:console -entry:entry -force:unresolved -out:%t/entry-undefined-weak-external.exe \
+# RUN:   %t/entry-weak-undefined.obj %t/entry-mangled.lib
+# RUN: llvm-readobj --file-headers %t/entry-undefined-weak-external.exe | FileCheck %s
+
+# CHECK: AddressOfEntryPoint: 0x1000
+
+#--- entry-weak.s
+.globl default_entry
+default_entry:
+	ret
+
+.weak entry
+entry = default_entry
+
+#--- entry-mangled.s
+.globl "?entry@@YAHXZ"
+"?entry@@YAHXZ":
+	jmp	does_not_exist
+
+#--- entry-weak-undefined.s
+.weak entry
+entry = does_not_exist
diff --git a/lld/test/COFF/subsystem-inference-weak-external.s b/lld/test/COFF/subsystem-inference-weak-external.s
new file mode 100644
--- /dev/null
+++ b/lld/test/COFF/subsystem-inference-weak-external.s
@@ -0,0 +1,38 @@
+# REQUIRES: x86
+# RUN: rm -rf %t && split-file %s %t
+
+## Ensure that weak externals are considered during subsystem inference.
+
+# RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t/cui.obj %t/cui.s
+# RUN: lld-link -out:%t/cui.exe %t/cui.obj
+# RUN: llvm-readobj --file-headers %t/cui.exe | FileCheck --check-prefix=CUI %s
+# RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t/gui.obj %t/gui.s
+# RUN: lld-link -out:%t/gui.exe %t/gui.obj
+# RUN: llvm-readobj --file-headers %t/gui.exe | FileCheck --check-prefix=GUI %s
+
+# CUI:     Subsystem: IMAGE_SUBSYSTEM_WINDOWS_CUI
+# GUI:     Subsystem: IMAGE_SUBSYSTEM_WINDOWS_GUI
+
+#--- cui.s
+.global default_main
+default_main:
+	ret
+
+.weak main
+main = default_main
+
+.global mainCRTStartup
+mainCRTStartup:
+	ret
+
+#--- gui.s
+.global default_WinMain
+default_WinMain:
+	ret
+
+.weak WinMain
+WinMain = default_WinMain
+
+.global WinMainCRTStartup
+WinMainCRTStartup:
+	ret