diff --git a/src/main/antlr3/com/joestelmach/natty/generated/DateLexer.g b/src/main/antlr3/com/joestelmach/natty/generated/DateLexer.g
index 5f85fa30..ae3c389f 100644
--- a/src/main/antlr3/com/joestelmach/natty/generated/DateLexer.g
+++ b/src/main/antlr3/com/joestelmach/natty/generated/DateLexer.g
@@ -8,9 +8,11 @@ lexer grammar DateLexer;
 
   @Override
   public void displayRecognitionError(String[] tokenNames, RecognitionException re) {
-    String message = getErrorHeader(re);
-    try { message += getErrorMessage(re, tokenNames); } catch(Exception e) {}
-    _logger.debug(message);
+    if (_logger.isDebugEnabled()) {
+      String message = getErrorHeader(re);
+      try { message += getErrorMessage(re, tokenNames); } catch(Exception e) {}
+      _logger.debug(message);
+    }
   }
 }
 
diff --git a/src/main/antlr3/com/joestelmach/natty/generated/DateParser.g b/src/main/antlr3/com/joestelmach/natty/generated/DateParser.g
index d3c99128..30b35810 100644
--- a/src/main/antlr3/com/joestelmach/natty/generated/DateParser.g
+++ b/src/main/antlr3/com/joestelmach/natty/generated/DateParser.g
@@ -46,9 +46,11 @@ tokens {
 
   @Override
   public void displayRecognitionError(String[] tokenNames, RecognitionException re) {
-    String message = getErrorHeader(re);
-    try { message += getErrorMessage(re, tokenNames); } catch(Exception e) {}
-    _logger.debug(message);
+    if (_logger.isDebugEnabled()) {
+      String message = getErrorHeader(re);
+      try { message += getErrorMessage(re, tokenNames); } catch(Exception e) {}
+      _logger.debug(message);
+    }
   }
 }
 
diff --git a/src/main/java/com/joestelmach/natty/IcsSearcher.java b/src/main/java/com/joestelmach/natty/IcsSearcher.java
index ddf058d3..5ec7985d 100644
--- a/src/main/java/com/joestelmach/natty/IcsSearcher.java
+++ b/src/main/java/com/joestelmach/natty/IcsSearcher.java
@@ -43,11 +43,11 @@ public Map<Integer, Date> findDates(int startYear, int endYear, String eventSumm
         _holidayCalendar = new CalendarBuilder().build(fin);
         
       } catch (IOException e) {
-        _logger.error("Couln't open " + _calendarFileName);
+        _logger.error("Couln't open {}", _calendarFileName);
         return holidays;
         
       } catch (ParserException e) {
-        _logger.error("Couln't parse " + _calendarFileName);
+        _logger.error("Couln't parse {}", _calendarFileName);
         return holidays;
       }
     }
@@ -59,7 +59,7 @@ public Map<Integer, Date> findDates(int startYear, int endYear, String eventSumm
       period = new Period(from, to);
       
     } catch (ParseException e) {
-      _logger.error("Invalid start or end year: " + startYear + ", " + endYear, e);
+      _logger.error("Invalid start or end year: {}, {}", startYear, endYear, e);
       return holidays;
     }
     
diff --git a/src/main/java/com/joestelmach/natty/Parser.java b/src/main/java/com/joestelmach/natty/Parser.java
index 9a0f666f..8bb41bca 100644
--- a/src/main/java/com/joestelmach/natty/Parser.java
+++ b/src/main/java/com/joestelmach/natty/Parser.java
@@ -204,7 +204,7 @@ private DateGroup singleParse(TokenStream stream, String fullText, Date referenc
 
       // we only continue if a meaningful syntax tree has been built
       if(tree.getChildCount() > 0) {
-        _logger.info("PARSE: " + tokenString.toString());
+        _logger.info("PARSE: {}", tokenString.toString());
 
         // rewrite the tree (temporary fix for http://www.antlr.org/jira/browse/ANTLR-427)
         CommonTreeNodeStream nodes = new CommonTreeNodeStream(tree);
@@ -218,7 +218,7 @@ private DateGroup singleParse(TokenStream stream, String fullText, Date referenc
         walker.setReferenceDate(referenceDate);
         walker.getState().setDefaultTimeZone(_defaultTimeZone);
         walker.parse();
-        _logger.info("AST: " + tree.toStringTree());
+        _logger.info("AST: {}", tree.toStringTree());
 
         // run through the results and append the parse information
         group = walker.getState().getDateGroup();
@@ -307,16 +307,18 @@ private List<TokenStream> collectTokenStreams(TokenStream stream) {
       addGroup(currentGroup, groups);
     }
     
-    _logger.info("STREAM: " + tokenString.toString());
+    _logger.info("STREAM: {}", tokenString.toString());
     List<TokenStream> streams = new ArrayList<TokenStream>();
     for(List<Token> group:groups) {
       if(!group.isEmpty()) {
-        StringBuilder builder = new StringBuilder();
-        builder.append("GROUP: ");
-        for (Token token : group) {
-          builder.append(DateParser.tokenNames[token.getType()]).append(" ");
+        if (_logger.isInfoEnabled()) {
+          StringBuilder builder = new StringBuilder();
+          builder.append("GROUP: ");
+          for (Token token : group) {
+            builder.append(DateParser.tokenNames[token.getType()]).append(" ");
+          }
+          _logger.info(builder.toString());
         }
-        _logger.info(builder.toString());
 
         streams.add(new CommonTokenStream(new NattyTokenSource(group)));
       }