--- a/mobile/android/base/java/org/mozilla/gecko/telemetry/stores/TelemetryJSONFilePingStore.java
+++ b/mobile/android/base/java/org/mozilla/gecko/telemetry/stores/TelemetryJSONFilePingStore.java
@@ -73,19 +73,30 @@ public class TelemetryJSONFilePingStore 
 
     private final File storeDir;
     private final FilenameFilter uuidFilenameFilter;
     private final FileLastModifiedComparator fileLastModifiedComparator = new FileLastModifiedComparator();
 
     @WorkerThread // Writes to disk
     public TelemetryJSONFilePingStore(final File storeDir, final String profileName) {
         super(profileName);
+        if (storeDir.exists() && !storeDir.isDirectory()) {
+            // An alternative is to create a new directory, but we wouldn't
+            // be able to access it later so it's better to throw.
+            throw new IllegalStateException("Store dir unexpectedly exists & is not a directory - cannot continue");
+        }
+
         this.storeDir = storeDir;
         this.storeDir.mkdirs();
         uuidFilenameFilter = new FilenameRegexFilter(UUIDUtil.UUID_PATTERN);
+
+        if (!this.storeDir.canRead() || !this.storeDir.canWrite() || !this.storeDir.canExecute()) {
+            throw new IllegalStateException("Cannot read, write, or execute store dir: " +
+                    this.storeDir.canRead() + " " + this.storeDir.canWrite() + " " + this.storeDir.canExecute());
+        }
     }
 
     @VisibleForTesting File getPingFile(final String docID) {
         return new File(storeDir, docID);
     }
 
     @Override
     public void storePing(final TelemetryPing ping) throws IOException {

--- a/mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/stores/TestTelemetryJSONFilePingStore.java
+++ b/mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/stores/TestTelemetryJSONFilePingStore.java
@@ -14,16 +14,17 @@ import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 import org.mozilla.gecko.background.testhelpers.TestRunner;
 import org.mozilla.gecko.sync.ExtendedJSONObject;
 import org.mozilla.gecko.telemetry.TelemetryPing;
 import org.mozilla.gecko.util.FileUtils;
 
 import java.io.File;
 import java.io.FileOutputStream;
+import java.io.FilenameFilter;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
 
 import static org.junit.Assert.*;
@@ -65,16 +66,43 @@ public class TestTelemetryJSONFilePingSt
 
     @Test
     public void testConstructorOnlyWritesToGivenDir() throws Exception {
         // Constructor is called in @Before method
         assertTrue("Store dir exists", testDir.exists());
         assertEquals("Temp dir contains one dir (the store dir)", 1, tempDir.getRoot().list().length);
     }
 
+    @Test(expected = IllegalStateException.class)
+    public void testConstructorStoreAlreadyExistsAsNonDirectory() throws Exception {
+        final File file = tempDir.newFile();
+        new TelemetryJSONFilePingStore(file, "profileName"); // expected to throw.
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testConstructorDirIsNotReadable() throws Exception {
+        final File dir = tempDir.newFolder();
+        dir.setReadable(false);
+        new TelemetryJSONFilePingStore(dir, "profileName"); // expected to throw.
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testConstructorDirIsNotWritable() throws Exception {
+        final File dir = tempDir.newFolder();
+        dir.setWritable(false);
+        new TelemetryJSONFilePingStore(dir, "profileName"); // expected to throw.
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testConstructorDirIsNotExecutable() throws Exception {
+        final File dir = tempDir.newFolder();
+        dir.setExecutable(false);
+        new TelemetryJSONFilePingStore(dir, "profileName"); // expected to throw.
+    }
+
     @Test
     public void testStorePingStoresCorrectData() throws Exception {
         assertStoreFileCount(0);
 
         final String expectedID = getDocID();
         final TelemetryPing expectedPing = new TelemetryPing("a/server/url", generateTelemetryPayload(), expectedID);
         testStore.storePing(expectedPing);