diff --git a/lld/wasm/InputChunks.cpp b/lld/wasm/InputChunks.cpp
--- a/lld/wasm/InputChunks.cpp
+++ b/lld/wasm/InputChunks.cpp
@@ -350,7 +350,7 @@
 
   // TODO(sbc): Encode the relocations in the data section and write a loop
   // here to apply them.
-  uint32_t segmentVA = outputSeg->startVA + outputSegmentOffset;
+  uint64_t segmentVA = outputSeg->startVA + outputSegmentOffset;
   for (const WasmRelocation &rel : relocations) {
     uint64_t offset = rel.Offset - getInputSectionOffset();
     uint64_t outputOffset = segmentVA + offset;
diff --git a/lld/wasm/OutputSections.cpp b/lld/wasm/OutputSections.cpp
--- a/lld/wasm/OutputSections.cpp
+++ b/lld/wasm/OutputSections.cpp
@@ -152,6 +152,7 @@
         initExpr.Opcode = WASM_OPCODE_GLOBAL_GET;
         initExpr.Value.Global = WasmSym::memoryBase->getGlobalIndex();
       } else {
+        // FIXME(wvo): I64?
         initExpr.Opcode = WASM_OPCODE_I32_CONST;
         initExpr.Value.Int32 = segment->startVA;
       }
diff --git a/lld/wasm/OutputSegment.h b/lld/wasm/OutputSegment.h
--- a/lld/wasm/OutputSegment.h
+++ b/lld/wasm/OutputSegment.h
@@ -37,7 +37,7 @@
   uint32_t initFlags = 0;
   uint32_t sectionOffset = 0;
   uint32_t alignment = 0;
-  uint32_t startVA = 0;
+  uint64_t startVA = 0;
   std::vector<InputSegment *> inputSegments;
 
   // Sum of the size of the all the input segments
diff --git a/lld/wasm/SymbolTable.h b/lld/wasm/SymbolTable.h
--- a/lld/wasm/SymbolTable.h
+++ b/lld/wasm/SymbolTable.h
@@ -82,7 +82,7 @@
                                     InputGlobal *global);
   DefinedFunction *addSyntheticFunction(StringRef name, uint32_t flags,
                                         InputFunction *function);
-  DefinedData *addOptionalDataSymbol(StringRef name, uint32_t value = 0);
+  DefinedData *addOptionalDataSymbol(StringRef name, uint64_t value = 0);
 
   void handleSymbolVariants();
   void handleWeakUndefines();
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -211,7 +211,7 @@
 // exported via the --export flag.  Otherwise we don't add the symbol and return
 // nullptr.
 DefinedData *SymbolTable::addOptionalDataSymbol(StringRef name,
-                                                uint32_t value) {
+                                                uint64_t value) {
   Symbol *s = find(name);
   if (!s && (config->exportAll || config->exportedSymbols.count(name) != 0))
     s = insertName(name).first;
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -354,8 +354,8 @@
   if (!isValidCIdentifier(name))
     return;
   LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << name << "\n");
-  uint32_t start = seg->startVA;
-  uint32_t stop = start + seg->size;
+  uint64_t start = seg->startVA;
+  uint64_t stop = start + seg->size;
   symtab->addOptionalDataSymbol(saver.save("__start_" + name), start);
   symtab->addOptionalDataSymbol(saver.save("__stop_" + name), stop);
 }
@@ -838,7 +838,12 @@
       for (const OutputSegment *s : segments) {
         if (needsPassiveInitialization(s)) {
           // destination address
-          writeI32Const(os, s->startVA, "destination address");
+          if (config->is64) {
+            writeI64Const(os, s->startVA, "destination address");
+          } else {
+            writeI32Const(os, static_cast<int32_t>(s->startVA),
+                          "destination address");
+          }
           // source segment offset
           writeI32Const(os, 0, "segment offset");
           // memory region size
@@ -960,6 +965,7 @@
       writeU8(os, WASM_OPCODE_GLOBAL_SET, "global.set");
       writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "global index");
 
+      // FIXME(wvo): this local needs to be I64 in wasm64, or we need an extend op.
       writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
       writeUleb128(os, 0, "local index");
 
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
@@ -39,7 +39,7 @@
 defm MEMORY_INIT_A#B :
   BULK_I<(outs),
          (ins i32imm_op:$seg, i32imm_op:$idx, rc:$dest,
-              rc:$offset, rc:$size),
+              I32:$offset, I32:$size),
          (outs), (ins i32imm_op:$seg, i32imm_op:$idx),
          [],
          "memory.init\t$seg, $idx, $dest, $offset, $size",