Index: lib/MC/WasmObjectWriter.cpp
===================================================================
--- lib/MC/WasmObjectWriter.cpp
+++ lib/MC/WasmObjectWriter.cpp
@@ -430,9 +430,13 @@
 
   if (SymA && SymA->isVariable()) {
     const MCExpr *Expr = SymA->getVariableValue();
-    const auto *Inner = cast<MCSymbolRefExpr>(Expr);
-    if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
-      llvm_unreachable("weakref used in reloc not yet implemented");
+    if (Expr->getKind() == MCExpr::SymbolRef) {
+      const auto *Inner = cast<MCSymbolRefExpr>(Expr);
+      if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
+        llvm_unreachable("weakref used in reloc not yet implemented");      
+    } else {
+      llvm_unreachable("expression kind not supported");
+    }
   }
 
   // Put any constant offset in an addend. Offsets can be negative, and
@@ -490,8 +494,12 @@
 static const MCSymbolWasm* ResolveSymbol(const MCSymbolWasm& Symbol) {
   if (Symbol.isVariable()) {
     const MCExpr *Expr = Symbol.getVariableValue();
-    auto *Inner = cast<MCSymbolRefExpr>(Expr);
-    return cast<MCSymbolWasm>(&Inner->getSymbol());
+    if (Expr->getKind() == MCExpr::SymbolRef) {    
+      auto *Inner = cast<MCSymbolRefExpr>(Expr);
+      return cast<MCSymbolWasm>(&Inner->getSymbol());
+    } else {
+      llvm_unreachable("expression kind not supported");      
+    }
   }
   return &Symbol;
 }