diff --git a/src/cmd/compile/internal/gc/pgen.go b/src/cmd/compile/internal/gc/pgen.go
index 63e58609505..1dc4b534271 100644
--- a/src/cmd/compile/internal/gc/pgen.go
+++ b/src/cmd/compile/internal/gc/pgen.go
@@ -243,6 +243,14 @@ func compile(fn *Node) {
 	// From this point, there should be no uses of Curfn. Enforce that.
 	Curfn = nil
 
+	if fn.funcname() == "_" {
+		// We don't need to generate code for this function, just report errors in its body.
+		// At this point we've generated any errors needed.
+		// (Beyond here we generate only non-spec errors, like "stack frame too large".)
+		// See issue 29870.
+		return
+	}
+
 	// Set up the function's LSym early to avoid data races with the assemblers.
 	fn.Func.initLSym(true)
 
diff --git a/test/fixedbugs/issue29870.go b/test/fixedbugs/issue29870.go
new file mode 100644
index 00000000000..b79860ca2bb
--- /dev/null
+++ b/test/fixedbugs/issue29870.go
@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2019 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.
+
+// Make sure we can compile "_" functions without crashing.
+
+package main
+
+import "log"
+
+func _() {
+	log.Println("%2F")
+}
diff --git a/test/fixedbugs/issue29870b.go b/test/fixedbugs/issue29870b.go
new file mode 100644
index 00000000000..1bac566bbbf
--- /dev/null
+++ b/test/fixedbugs/issue29870b.go
@@ -0,0 +1,14 @@
+// errorcheck
+
+// Copyright 2019 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.
+
+// Make sure we're compiling "_" functions at least enough
+// to get to an error which is generated during walk.
+
+package main
+
+func _() {
+	x := 7 // ERROR "x declared and not used"
+}