diff --git a/cmd/guru/main.go b/cmd/guru/main.go
index 761828a..8e4af00 100644
--- a/cmd/guru/main.go
+++ b/cmd/guru/main.go
@@ -19,6 +19,8 @@
 	"io"
 	"log"
 	"os"
+	"path/filepath"
+	"runtime"
 	"runtime/pprof"
 	"strings"
 	"sync"
@@ -38,6 +40,14 @@
 
 func init() {
 	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags", buildutil.TagsFlagDoc)
+
+	// gccgo does not provide a GOROOT with standard library sources.
+	// If we have one in the environment, force gc mode.
+	if build.Default.Compiler == "gccgo" {
+		if _, err := os.Stat(filepath.Join(runtime.GOROOT(), "src", "runtime", "runtime.go")); err == nil {
+			build.Default.Compiler = "gc"
+		}
+	}
 }
 
 const useHelp = "Run 'guru -help' for more information.\n"