diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index 5c5503619f..19f109055d 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -737,6 +737,9 @@ func typefmt(t *Type, flag FmtFlag) string {
 			Fatalf("cannot use TDDDFIELD with old exporter")
 		}
 		return fmt.Sprintf("%v <%v> %v", Econv(t.Etype), t.Sym, t.DDDField())
+
+	case Txxx:
+		return "Txxx"
 	}
 
 	if fmtmode == FExp {
diff --git a/src/cmd/compile/internal/gc/racewalk.go b/src/cmd/compile/internal/gc/racewalk.go
index 09889a40f3..f6e65146d6 100644
--- a/src/cmd/compile/internal/gc/racewalk.go
+++ b/src/cmd/compile/internal/gc/racewalk.go
@@ -164,7 +164,13 @@ func instrumentnode(np **Node, init *Nodes, wr int, skip int) {
 				var outn Nodes
 				outn.Set(out)
 				instrumentnode(&ls[i], &outn, 0, 0)
-				out = append(outn.Slice(), ls[i])
+				if ls[i].Op != OAS || ls[i].Ninit.Len() == 0 {
+					out = append(outn.Slice(), ls[i])
+				} else {
+					// Splice outn onto end of ls[i].Ninit
+					ls[i].Ninit.AppendNodes(&outn)
+					out = append(out, ls[i])
+				}
 			}
 		}
 		n.List.Set(out)
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 90c4d4e95e..7c5f906d76 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3699,6 +3699,10 @@ func (s *state) resolveFwdRef(v *ssa.Value) {
 	if b == s.f.Entry {
 		// Live variable at start of function.
 		if s.canSSA(name) {
+			if strings.HasPrefix(name.Sym.Name, "autotmp_") {
+				// It's likely that this is an uninitialized variable in the entry block.
+				s.Fatalf("Treating auto as if it were arg, func %s, node %v, value %v", b.Func.Name, name, v)
+			}
 			v.Op = ssa.OpArg
 			v.Aux = name
 			return
diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index 22b9d12c19..aec23a1368 100644
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -417,7 +417,7 @@ func (s *regAllocState) allocValToReg(v *Value, mask regMask, nospill bool, line
 		// Load v from its spill location.
 		case vi.spill != nil:
 			if s.f.pass.debug > logSpills {
-				s.f.Config.Warnl(vi.spill.Line, "load spill")
+				s.f.Config.Warnl(vi.spill.Line, "load spill for %v from %v", v, vi.spill)
 			}
 			c = s.curBlock.NewValue1(line, OpLoadReg, v.Type, vi.spill)
 			vi.spillUsed = true
@@ -1078,7 +1078,7 @@ func (s *regAllocState) regalloc(f *Func) {
 		vi := s.values[i]
 		if vi.spillUsed {
 			if s.f.pass.debug > logSpills {
-				s.f.Config.Warnl(vi.spill.Line, "spilled value")
+				s.f.Config.Warnl(vi.spill.Line, "spilled value at %v remains", vi.spill)
 			}
 			continue
 		}
diff --git a/test/fixedbugs/issue15091.go b/test/fixedbugs/issue15091.go
new file mode 100644
index 0000000000..346e906171
--- /dev/null
+++ b/test/fixedbugs/issue15091.go
@@ -0,0 +1,25 @@
+// errorcheck -0 -race
+
+// Copyright 2016 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sample
+
+type Html struct {
+	headerIDs map[string]int
+}
+
+// We don't want to see:
+//    internal error: (*Html).xyzzy autotmp_3 (type *int) recorded as live on entry, p.Pc=0
+// or (now, with the error caught earlier)
+//    Treating auto as if it were arg, func (*Html).xyzzy, node ...
+// caused by racewalker inserting instrumentation before an OAS where the Ninit
+// of the OAS defines part of its right-hand-side. (I.e., the race instrumentation
+// references a variable before it is defined.)
+func (options *Html) xyzzy(id string) string {
+	for count, found := options.headerIDs[id]; found; count, found = options.headerIDs[id] {
+		_ = count
+	}
+	return ""
+}