diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 265873a3ab..96cf2177a6 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3029,10 +3029,9 @@ func (s *state) insertWBmove(t *Type, left, right *ssa.Value, line int32) {
 
 	aux := &ssa.ExternSymbol{Typ: Types[TBOOL], Sym: syslook("writeBarrier").Sym}
 	flagaddr := s.newValue1A(ssa.OpAddr, Ptrto(Types[TUINT32]), aux, s.sb)
-	// TODO: select the .enabled field. It is currently first, so not needed for now.
-	// Load word, test byte, avoiding partial register write from load byte.
+	// Load word, test word, avoiding partial register write from load byte.
 	flag := s.newValue2(ssa.OpLoad, Types[TUINT32], flagaddr, s.mem())
-	flag = s.newValue1(ssa.OpTrunc64to8, Types[TBOOL], flag)
+	flag = s.newValue2(ssa.OpNeq32, Types[TBOOL], flag, s.constInt32(Types[TUINT32], 0))
 	b := s.endBlock()
 	b.Kind = ssa.BlockIf
 	b.Likely = ssa.BranchUnlikely
@@ -3080,10 +3079,9 @@ func (s *state) insertWBstore(t *Type, left, right *ssa.Value, line int32, skip
 
 	aux := &ssa.ExternSymbol{Typ: Types[TBOOL], Sym: syslook("writeBarrier").Sym}
 	flagaddr := s.newValue1A(ssa.OpAddr, Ptrto(Types[TUINT32]), aux, s.sb)
-	// TODO: select the .enabled field. It is currently first, so not needed for now.
-	// Load word, test byte, avoiding partial register write from load byte.
+	// Load word, test word, avoiding partial register write from load byte.
 	flag := s.newValue2(ssa.OpLoad, Types[TUINT32], flagaddr, s.mem())
-	flag = s.newValue1(ssa.OpTrunc64to8, Types[TBOOL], flag)
+	flag = s.newValue2(ssa.OpNeq32, Types[TBOOL], flag, s.constInt32(Types[TUINT32], 0))
 	b := s.endBlock()
 	b.Kind = ssa.BlockIf
 	b.Likely = ssa.BranchUnlikely
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index ae8338ac10..c497ccee67 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -220,10 +220,11 @@ var gcphase uint32
 // The compiler knows about this variable.
 // If you change it, you must change the compiler too.
 var writeBarrier struct {
-	enabled bool   // compiler emits a check of this before calling write barrier
-	needed  bool   // whether we need a write barrier for current GC phase
-	cgo     bool   // whether we need a write barrier for a cgo check
-	alignme uint64 // guarantee alignment so that compiler can use a 32 or 64-bit load
+	enabled bool    // compiler emits a check of this before calling write barrier
+	pad     [3]byte // compiler uses 32-bit load for "enabled" field
+	needed  bool    // whether we need a write barrier for current GC phase
+	cgo     bool    // whether we need a write barrier for a cgo check
+	alignme uint64  // guarantee alignment so that compiler can use a 32 or 64-bit load
 }
 
 // gcBlackenEnabled is 1 if mutator assists and background mark