diff --git a/go/analysis/internal/analysisflags/flags.go b/go/analysis/internal/analysisflags/flags.go
index a03a185..062d062 100644
--- a/go/analysis/internal/analysisflags/flags.go
+++ b/go/analysis/internal/analysisflags/flags.go
@@ -8,6 +8,7 @@
 
 import (
 	"crypto/sha256"
+	"encoding/gob"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -32,6 +33,14 @@
 // including (in multi mode) a flag named after the analyzer,
 // parses the flags, then filters and returns the list of
 // analyzers enabled by flags.
+//
+// The result is intended to be passed to unitchecker.Run or checker.Run.
+// Use in unitchecker.Run will gob.Register all fact types for the returned
+// graph of analyzers but of course not the ones only reachable from
+// dropped analyzers. To avoid inconsistency about which gob types are
+// registered from run to run, Parse itself gob.Registers all the facts
+// only reachable from dropped analyzers.
+// This is not a particularly elegant API, but this is an internal package.
 func Parse(analyzers []*analysis.Analyzer, multi bool) []*analysis.Analyzer {
 	// Connect each analysis flag to the command line as -analysis.flag.
 	enabled := make(map[*analysis.Analyzer]*triState)
@@ -88,6 +97,8 @@
 		os.Exit(0)
 	}
 
+	everything := expand(analyzers)
+
 	// If any -NAME flag is true,  run only those analyzers. Otherwise,
 	// if any -NAME flag is false, run all but those analyzers.
 	if multi {
@@ -119,9 +130,35 @@
 		}
 	}
 
+	// Register fact types of skipped analyzers
+	// in case we encounter them in imported files.
+	kept := expand(analyzers)
+	for a := range everything {
+		if !kept[a] {
+			for _, f := range a.FactTypes {
+				gob.Register(f)
+			}
+		}
+	}
+
 	return analyzers
 }
 
+func expand(analyzers []*analysis.Analyzer) map[*analysis.Analyzer]bool {
+	seen := make(map[*analysis.Analyzer]bool)
+	var visitAll func([]*analysis.Analyzer)
+	visitAll = func(analyzers []*analysis.Analyzer) {
+		for _, a := range analyzers {
+			if !seen[a] {
+				seen[a] = true
+				visitAll(a.Requires)
+			}
+		}
+	}
+	visitAll(analyzers)
+	return seen
+}
+
 func printFlags() {
 	type jsonFlag struct {
 		Name  string