diff --git a/java/hiddenapi_modular.go b/java/hiddenapi_modular.go
index 44cdfa5..534a814 100644
--- a/java/hiddenapi_modular.go
+++ b/java/hiddenapi_modular.go
@@ -295,6 +295,12 @@
 	return dexJar.Path()
 }
 
+// HIDDENAPI_STUB_FLAGS_IMPL_FLAGS is the set of flags that identify implementation only signatures,
+// i.e. those signatures that are not part of any API (including the hidden API).
+var HIDDENAPI_STUB_FLAGS_IMPL_FLAGS = []string{}
+
+var HIDDENAPI_FLAGS_CSV_IMPL_FLAGS = []string{"blocked"}
+
 // buildRuleToGenerateHiddenAPIStubFlagsFile creates a rule to create a hidden API stub flags file.
 //
 // The rule is initialized but not built so that the caller can modify it and select an appropriate
@@ -345,7 +351,8 @@
 	// If there are stub flag files that have been generated by fragments on which this depends then
 	// use them to validate the stub flag file generated by the rules created by this method.
 	if len(stubFlagSubsets) > 0 {
-		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, stubFlagSubsets)
+		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, stubFlagSubsets,
+			HIDDENAPI_STUB_FLAGS_IMPL_FLAGS)
 
 		// Add the file that indicates that the file generated by this is valid.
 		//
@@ -904,7 +911,8 @@
 	// If there are flag files that have been generated by fragments on which this depends then use
 	// them to validate the flag file generated by the rules created by this method.
 	if len(flagSubsets) > 0 {
-		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, flagSubsets)
+		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, flagSubsets,
+			HIDDENAPI_FLAGS_CSV_IMPL_FLAGS)
 
 		// Add the file that indicates that the file generated by this is valid.
 		//
@@ -968,13 +976,29 @@
 	return patternsFile
 }
 
-// buildRuleRemoveBlockedFlag creates a rule that will remove entries from the input path which
-// only have blocked flags. It will not remove entries that have blocked as well as other flags,
-// e.g. blocked,core-platform-api.
-func buildRuleRemoveBlockedFlag(ctx android.BuilderContext, name string, desc string, inputPath android.Path, filteredPath android.WritablePath) {
+// buildRuleRemoveSignaturesWithImplementationFlags creates a rule that will remove signatures from
+// the input flags file which have only the implementation flags, i.e. are not part of an API.
+//
+// The implementationFlags specifies the set of default flags that identifies the signature of a
+// private, implementation only, member. Signatures that match those flags are removed from the
+// flags as they are implementation only.
+//
+// This is used to remove implementation only signatures from the signature files that are persisted
+// in the sdk snapshot as the sdk snapshots should not include implementation details. The
+// signatures generated by this method will be compared by the buildRuleValidateOverlappingCsvFiles
+// method which treats any missing signatures as if they were implementation only signatures.
+func buildRuleRemoveSignaturesWithImplementationFlags(ctx android.BuilderContext,
+	name string, desc string, inputPath android.Path, filteredPath android.WritablePath,
+	implementationFlags []string) {
+
 	rule := android.NewRuleBuilder(pctx, ctx)
+	implementationFlagPattern := ""
+	for _, implementationFlag := range implementationFlags {
+		implementationFlagPattern = implementationFlagPattern + "," + implementationFlag
+	}
 	rule.Command().
-		Text(`grep -vE "^[^,]+,blocked$"`).Input(inputPath).Text(">").Output(filteredPath).
+		Text(`grep -vE "^[^,]+` + implementationFlagPattern + `$"`).Input(inputPath).
+		Text(">").Output(filteredPath).
 		// Grep's exit code depends on whether it finds anything. It is 0 (build success) when it finds
 		// something and 1 (build failure) when it does not and 2 (when it encounters an error).
 		// However, while it is unlikely it is not an error if this does not find any matches. The
@@ -986,7 +1010,14 @@
 
 // buildRuleValidateOverlappingCsvFiles checks that the modular CSV files, i.e. the files generated
 // by the individual bootclasspath_fragment modules are subsets of the monolithic CSV file.
-func buildRuleValidateOverlappingCsvFiles(ctx android.BuilderContext, name string, desc string, monolithicFilePath android.WritablePath, csvSubsets SignatureCsvSubsets) android.WritablePath {
+//
+// The implementationFlags specifies the set of default flags that identifies the signature of a
+// private, implementation only, member. A signature which is present in a monolithic flags subset
+// defined by SignatureCsvSubset but which is not present in the flags file from the corresponding
+// module is assumed to be an implementation only member and so must have these flags.
+func buildRuleValidateOverlappingCsvFiles(ctx android.BuilderContext, name string, desc string,
+	monolithicFilePath android.WritablePath, csvSubsets SignatureCsvSubsets,
+	implementationFlags []string) android.WritablePath {
 	// The file which is used to record that the flags file is valid.
 	validFile := pathForValidation(ctx, monolithicFilePath)
 
@@ -1003,6 +1034,10 @@
 			Implicit(subset.CsvFile).Implicit(subset.SignaturePatternsFile)
 	}
 
+	for _, implementationFlag := range implementationFlags {
+		command.FlagWithArg("--implementation-flag ", implementationFlag)
+	}
+
 	// If validation passes then update the file that records that.
 	command.Text("&& touch").Output(validFile)
 	rule.Build(name+"Validation", desc+" validation")
@@ -1076,12 +1111,16 @@
 	// Generate the filtered-stub-flags.csv file which contains the filtered stub flags that will be
 	// compared against the monolithic stub flags.
 	filteredStubFlagsCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "filtered-stub-flags.csv")
-	buildRuleRemoveBlockedFlag(ctx, "modularHiddenApiFilteredStubFlags", "modular hiddenapi filtered stub flags", stubFlagsCSV, filteredStubFlagsCSV)
+	buildRuleRemoveSignaturesWithImplementationFlags(ctx, "modularHiddenApiFilteredStubFlags",
+		"modular hiddenapi filtered stub flags", stubFlagsCSV, filteredStubFlagsCSV,
+		HIDDENAPI_STUB_FLAGS_IMPL_FLAGS)
 
 	// Generate the filtered-flags.csv file which contains the filtered flags that will be compared
 	// against the monolithic flags.
 	filteredFlagsCSV := android.PathForModuleOut(ctx, hiddenApiSubDir, "filtered-flags.csv")
-	buildRuleRemoveBlockedFlag(ctx, "modularHiddenApiFilteredFlags", "modular hiddenapi filtered flags", allFlagsCSV, filteredFlagsCSV)
+	buildRuleRemoveSignaturesWithImplementationFlags(ctx, "modularHiddenApiFilteredFlags",
+		"modular hiddenapi filtered flags", allFlagsCSV, filteredFlagsCSV,
+		HIDDENAPI_FLAGS_CSV_IMPL_FLAGS)
 
 	// Store the paths in the info for use by other modules and sdk snapshot generation.
 	output := HiddenAPIOutput{