diff --git a/lld/test/wasm/shared.ll b/lld/test/wasm/shared.ll
--- a/lld/test/wasm/shared.ll
+++ b/lld/test/wasm/shared.ll
@@ -13,10 +13,12 @@
   ; To ensure we use __stack_pointer
   %ptr = alloca i32
   %0 = load i32, i32* @data, align 4
-  %1 = load i32, i32* @data_external, align 4
-  %2 = load i32 ()*, i32 ()** @indirect_func, align 4
-  call i32 %2()
-  ret i32 %1
+  ; TODO(sbc): Re-enable once the codegen supports generating the correct
+  ; relocation type when referencing external data in shared libraries.
+  ; %1 = load i32, i32* @data_external, align 4
+  %1 = load i32 ()*, i32 ()** @indirect_func, align 4
+  call i32 %1()
+  ret i32 %0
 }
 
 declare void @func_external()
@@ -29,7 +31,7 @@
 ; CHECK:      Sections:
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            dylink
-; CHECK-NEXT:     MemorySize:      8
+; CHECK-NEXT:     MemorySize:      12
 ; CHECK-NEXT:     MemoryAlignment: 2
 ; CHECK-NEXT:     TableSize:       2
 ; CHECK-NEXT:     TableAlignment:  0
@@ -60,11 +62,11 @@
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         GlobalType:      I32
 ; CHECK-NEXT:         GlobalMutable:   false
-; CHECK-NEXT:       - Module:          env
-; CHECK-NEXT:         Field:           data_external
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         GlobalType:      I32
-; CHECK-NEXT:         GlobalMutable:   true
+; XCHECK-NEXT:       - Module:          env
+; XCHECK-NEXT:         Field:           data_external
+; XCHECK-NEXT:         Kind:            GLOBAL
+; XCHECK-NEXT:         GlobalType:      I32
+; XCHECK-NEXT:         GlobalMutable:   true
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           func_external
 ; CHECK-NEXT:         Kind:            FUNCTION
@@ -88,4 +90,4 @@
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          GLOBAL_GET
 ; CHECK-NEXT:           Index:           1
-; CHECK-NEXT:         Content:         '0000000001000000'
+; CHECK-NEXT:         Content:         '020000000000000001000000'
diff --git a/lld/test/wasm/undefined-data.ll b/lld/test/wasm/undefined-data.ll
new file mode 100644
--- /dev/null
+++ b/lld/test/wasm/undefined-data.ll
@@ -0,0 +1,16 @@
+; RUN: llc -filetype=obj %s -o %t.o
+; RUN: not wasm-ld -o %t.wasm %t.o 2>&1 | FileCheck %s -check-prefix=UNDEF
+; RUN: not wasm-ld --allow-undefined -o %t.wasm %t.o 2>&1 | FileCheck %s -check-prefix=BADRELOC
+
+target triple = "wasm32-unknown-unknown"
+
+@data_external = external global i32
+
+define i32 @_start() {
+entry:
+    %0 = load i32, i32* @data_external, align 4
+    ret i32 %0
+}
+
+; UNDEF: undefined symbol: data_external
+; BADRELOC: undefined-data.ll.tmp.o: relocation of type R_WASM_MEMORY_* against undefined data symbol: data_external
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -1041,17 +1041,32 @@
     ObjFile *File = Chunk->File;
     ArrayRef<WasmSignature> Types = File->getWasmObj()->types();
     for (const WasmRelocation &Reloc : Chunk->getRelocations()) {
-      if (Reloc.Type == R_WASM_TABLE_INDEX_I32 ||
-          Reloc.Type == R_WASM_TABLE_INDEX_SLEB) {
+      switch (Reloc.Type) {
+      case R_WASM_TABLE_INDEX_I32:
+      case R_WASM_TABLE_INDEX_SLEB: {
         FunctionSymbol *Sym = File->getFunctionSymbol(Reloc.Index);
         if (Sym->hasTableIndex() || !Sym->hasFunctionIndex())
           continue;
         Sym->setTableIndex(TableIndex++);
         IndirectFunctions.emplace_back(Sym);
-      } else if (Reloc.Type == R_WASM_TYPE_INDEX_LEB) {
+        break;
+      }
+      case R_WASM_TYPE_INDEX_LEB:
         // Mark target type as live
         File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
         File->TypeIsUsed[Reloc.Index] = true;
+        break;
+      case R_WASM_MEMORY_ADDR_SLEB:
+      case R_WASM_MEMORY_ADDR_I32:
+      case R_WASM_MEMORY_ADDR_LEB: {
+        DataSymbol* DataSym = File->getDataSymbol(Reloc.Index);
+        if (!Config->Relocatable && !isa<DefinedData>(DataSym) && !DataSym->isWeak())
+          error(File->getName() +
+                ": relocation of type R_WASM_MEMORY_* against undefined data "
+                "symbol: " +
+                DataSym->getName());
+        break;
+      }
       }
     }
   };