diff --git a/src/org/linphone/LinphoneActivity.java b/src/org/linphone/LinphoneActivity.java
index 05315dea1..eb4a7e6d2 100644
--- a/src/org/linphone/LinphoneActivity.java
+++ b/src/org/linphone/LinphoneActivity.java
@@ -1041,7 +1041,7 @@ public class LinphoneActivity extends FragmentActivity implements OnClickListene
 		}
 	}
 	
-	private void prepareContactsInBackground() {
+	private synchronized void prepareContactsInBackground() {
 		if (contactCursor != null) {
 			contactCursor.close();
 		}
diff --git a/src/org/linphone/LinphoneUtils.java b/src/org/linphone/LinphoneUtils.java
index e64e5e905..e969de7fd 100644
--- a/src/org/linphone/LinphoneUtils.java
+++ b/src/org/linphone/LinphoneUtils.java
@@ -29,6 +29,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 import org.linphone.core.LinphoneAddress;
@@ -69,12 +70,14 @@ public final class LinphoneUtils {
 
 	public static boolean isSipAddress(String numberOrAddress) {
 		Pattern p = Pattern.compile(sipAddressRegExp);
-		return p.matcher(numberOrAddress).matches();
+		Matcher m = p.matcher(numberOrAddress);
+		return m != null && m.matches();
 	}
 	
 	public static boolean isStrictSipAddress(String numberOrAddress) {
 		Pattern p = Pattern.compile(strictSipAddressRegExp);
-		return p.matcher(numberOrAddress).matches();
+		Matcher m = p.matcher(numberOrAddress);
+		return m != null && m.matches();
 	}
 	
 	public static String getUsernameFromAddress(String address) {
diff --git a/src/org/linphone/compatibility/ApiFivePlus.java b/src/org/linphone/compatibility/ApiFivePlus.java
index 328292a72..0652d0b8c 100644
--- a/src/org/linphone/compatibility/ApiFivePlus.java
+++ b/src/org/linphone/compatibility/ApiFivePlus.java
@@ -302,17 +302,23 @@ public class ApiFivePlus {
 		Contact contact = getContact(cr, cursor, 0);
 		if (contact != null && contact.getNumerosOrAddresses().contains(sipUri)) {
 			address.setDisplayName(contact.getName());
+			cursor.close();
 			return contact.getPhotoUri();
 		}
-		
+
+		cursor.close();
 		return null;
 	}
 
 	public static String refreshContactName(ContentResolver cr, String id) {
-		Cursor c = getGeneralContactCursor(cr, Data.CONTACT_ID + " = '" + id + "'", false);
-		if (c != null && c.moveToFirst()) {
-			return getContactDisplayName(c);
+		Cursor cursor = getGeneralContactCursor(cr, Data.CONTACT_ID + " = '" + id + "'", false);
+		if (cursor != null && cursor.moveToFirst()) {
+			String contactDisplayName = getContactDisplayName(cursor);
+			cursor.close();
+			return contactDisplayName;
 		}
+		
+		cursor.close();
 		return null;
 	}