diff --git a/lld/test/wasm/Inputs/weak-undefined.s b/lld/test/wasm/Inputs/weak-undefined.s
new file mode 100644
--- /dev/null
+++ b/lld/test/wasm/Inputs/weak-undefined.s
@@ -0,0 +1,2 @@
+.functype foo () -> ()
+.weak foo
diff --git a/lld/test/wasm/weak-and-strong-undef.s b/lld/test/wasm/weak-and-strong-undef.s
new file mode 100644
--- /dev/null
+++ b/lld/test/wasm/weak-and-strong-undef.s
@@ -0,0 +1,18 @@
+# Test that when a symbol (foo) is both weakly and stronly undefined the
+# string undefined symbol alwaeys generates an error, whichever object
+# file is seen first.
+
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %S/Inputs/weak-undefined.s -o %t2.o
+# RUN: not wasm-ld %t1.o %t2.o -o /dev/null 2>&1 | FileCheck %s
+# RUN: not wasm-ld %t2.o %t1.o -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: undefined symbol: foo
+
+_start:
+    .globl _start
+    .functype _start () -> ()
+    call foo
+    end_function
+
+.functype foo () -> ()
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -426,6 +426,12 @@
             toString(existing->getFile()) + "\n>>> defined as " +
             *importModule + " in " + toString(file));
   }
+
+  // Update symbol binding, if the existing symbols is weak
+  uint32_t binding = existing->flags & WASM_SYMBOL_BINDING_MASK;
+  if (existing->isWeak() && binding != WASM_SYMBOL_BINDING_WEAK) {
+    existing->flags = (existing->flags & ~WASM_SYMBOL_BINDING_MASK) | binding;
+  }
 }
 
 Symbol *SymbolTable::addUndefinedFunction(StringRef name,
@@ -436,7 +442,8 @@
                                           bool isCalledDirectly) {
   LLVM_DEBUG(dbgs() << "addUndefinedFunction: " << name << " ["
                     << (sig ? toString(*sig) : "none")
-                    << "] IsCalledDirectly:" << isCalledDirectly << "\n");
+                    << "] IsCalledDirectly:" << isCalledDirectly 
+                    << " flags=0x" << utohexstr(flags) << "\n");
   assert(flags & WASM_SYMBOL_UNDEFINED);
 
   Symbol *s;
@@ -460,9 +467,9 @@
       reportTypeError(s, file, WASM_SYMBOL_TYPE_FUNCTION);
       return s;
     }
-    auto *existingUndefined = dyn_cast<UndefinedFunction>(existingFunction);
     if (!existingFunction->signature && sig)
       existingFunction->signature = sig;
+    auto *existingUndefined = dyn_cast<UndefinedFunction>(existingFunction);
     if (isCalledDirectly && !signatureMatches(existingFunction, sig)) {
       // If the existing undefined functions is not called direcltly then let
       // this one take precedence.  Otherwise the existing function is either
@@ -634,7 +641,7 @@
   auto *func = make<SyntheticFunction>(sig, sym->getName(), debugName);
   func->setBody(unreachableFn);
   syntheticFunctions.emplace_back(func);
-  replaceSymbol<DefinedFunction>(sym, sym->getName(), sym->getFlags(), nullptr,
+  replaceSymbol<DefinedFunction>(sym, sym->getName(), sym->flags, nullptr,
                                  func);
   return func;
 }
diff --git a/lld/wasm/Symbols.h b/lld/wasm/Symbols.h
--- a/lld/wasm/Symbols.h
+++ b/lld/wasm/Symbols.h
@@ -86,8 +86,6 @@
   // Returns the file from which this symbol was created.
   InputFile *getFile() const { return file; }
 
-  uint32_t getFlags() const { return flags; }
-
   InputChunk *getChunk() const;
 
   // Indicates that the section or import for this symbol will be included in
@@ -124,14 +122,13 @@
 
 protected:
   Symbol(StringRef name, Kind k, uint32_t flags, InputFile *f)
-      : name(name), file(f), flags(flags), symbolKind(k),
+      : name(name), file(f), symbolKind(k),
         referenced(!config->gcSections), requiresGOT(false),
         isUsedInRegularObj(false), forceExport(false), canInline(false),
-        traced(false) {}
+        traced(false), flags(flags) {}
 
   StringRef name;
   InputFile *file;
-  uint32_t flags;
   uint32_t outputSymbolIndex = INVALID_INDEX;
   uint32_t gotIndex = INVALID_INDEX;
   Kind symbolKind;
@@ -160,6 +157,8 @@
 
   // True if this symbol is specified by --trace-symbol option.
   bool traced : 1;
+
+  uint32_t flags;
 };
 
 class FunctionSymbol : public Symbol {
diff --git a/lld/wasm/SyntheticSections.cpp b/lld/wasm/SyntheticSections.cpp
--- a/lld/wasm/SyntheticSections.cpp
+++ b/lld/wasm/SyntheticSections.cpp
@@ -391,7 +391,7 @@
     for (const Symbol *sym : symtabEntries) {
       assert(sym->isDefined() || sym->isUndefined());
       WasmSymbolType kind = sym->getWasmType();
-      uint32_t flags = sym->getFlags();
+      uint32_t flags = sym->flags;
 
       writeU8(sub.os, kind, "sym kind");
       writeUleb128(sub.os, flags, "sym flags");