diff --git a/bazel/aquery.go b/bazel/aquery.go
index 404be8c..a196e8b 100644
--- a/bazel/aquery.go
+++ b/bazel/aquery.go
@@ -83,11 +83,15 @@
 // AqueryBuildStatements returns an array of BuildStatements which should be registered (and output
 // to a ninja file) to correspond one-to-one with the given action graph json proto (from a bazel
 // aquery invocation).
-func AqueryBuildStatements(aqueryJsonProto []byte) []BuildStatement {
+func AqueryBuildStatements(aqueryJsonProto []byte) ([]BuildStatement, error) {
 	buildStatements := []BuildStatement{}
 
 	var aqueryResult actionGraphContainer
-	json.Unmarshal(aqueryJsonProto, &aqueryResult)
+	err := json.Unmarshal(aqueryJsonProto, &aqueryResult)
+
+	if err != nil {
+		return nil, err
+	}
 
 	pathFragments := map[int]pathFragment{}
 	for _, pathFragment := range aqueryResult.PathFragments {
@@ -97,8 +101,7 @@
 	for _, artifact := range aqueryResult.Artifacts {
 		artifactPath, err := expandPathFragment(artifact.PathFragmentId, pathFragments)
 		if err != nil {
-			// TODO(cparsons): Better error handling.
-			panic(err.Error())
+			return nil, err
 		}
 		artifactIdToPath[artifact.Id] = artifactPath
 	}
@@ -110,15 +113,24 @@
 	for _, actionEntry := range aqueryResult.Actions {
 		outputPaths := []string{}
 		for _, outputId := range actionEntry.OutputIds {
-			// TODO(cparsons): Validate the id is present.
-			outputPaths = append(outputPaths, artifactIdToPath[outputId])
+			outputPath, exists := artifactIdToPath[outputId]
+			if !exists {
+				return nil, fmt.Errorf("undefined outputId %d", outputId)
+			}
+			outputPaths = append(outputPaths, outputPath)
 		}
 		inputPaths := []string{}
 		for _, inputDepSetId := range actionEntry.InputDepSetIds {
-			// TODO(cparsons): Validate the id is present.
-			for _, inputId := range depsetIdToArtifactIds[inputDepSetId] {
-				// TODO(cparsons): Validate the id is present.
-				inputPaths = append(inputPaths, artifactIdToPath[inputId])
+			inputArtifacts, exists := depsetIdToArtifactIds[inputDepSetId]
+			if !exists {
+				return nil, fmt.Errorf("undefined input depsetId %d", inputDepSetId)
+			}
+			for _, inputId := range inputArtifacts {
+				inputPath, exists := artifactIdToPath[inputId]
+				if !exists {
+					return nil, fmt.Errorf("undefined input artifactId %d", inputId)
+				}
+				inputPaths = append(inputPaths, inputPath)
 			}
 		}
 		buildStatement := BuildStatement{
@@ -130,7 +142,7 @@
 		buildStatements = append(buildStatements, buildStatement)
 	}
 
-	return buildStatements
+	return buildStatements, nil
 }
 
 func expandPathFragment(id int, pathFragmentsMap map[int]pathFragment) (string, error) {
@@ -140,7 +152,7 @@
 	for currId > 0 {
 		currFragment, ok := pathFragmentsMap[currId]
 		if !ok {
-			return "", fmt.Errorf("undefined path fragment id '%s'", currId)
+			return "", fmt.Errorf("undefined path fragment id %d", currId)
 		}
 		labels = append([]string{currFragment.Label}, labels...)
 		currId = currFragment.ParentId