diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 42b02c8..f15ff16 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -1575,6 +1575,9 @@
 // 	GOCACHE
 // 		The directory where the go command will store cached
 // 		information for reuse in future builds.
+// 	GODEBUG
+// 		Enable various debugging facilities. See 'go doc runtime'
+// 		for details.
 // 	GOENV
 // 		The location of the Go environment configuration file.
 // 		Cannot be set using 'go env -w'.
diff --git a/src/cmd/go/internal/help/helpdoc.go b/src/cmd/go/internal/help/helpdoc.go
index c2b5fb4..dfb89d4 100644
--- a/src/cmd/go/internal/help/helpdoc.go
+++ b/src/cmd/go/internal/help/helpdoc.go
@@ -493,6 +493,9 @@
 	GOCACHE
 		The directory where the go command will store cached
 		information for reuse in future builds.
+	GODEBUG
+		Enable various debugging facilities. See 'go doc runtime'
+		for details.
 	GOENV
 		The location of the Go environment configuration file.
 		Cannot be set using 'go env -w'.