diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreator.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreator.java
index 04280261b26..a0e00ebf733 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreator.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreator.java
@@ -25,14 +25,15 @@ import java.util.regex.Pattern;
  */
 public final class GrokPatternCreator {
 
-    private static String PREFACE = "preface";
-    private static String EPILOGUE = "epilogue";
+    private static final String PREFACE = "preface";
+    private static final String EPILOGUE = "epilogue";
 
     /**
      * The first match in this list will be chosen, so it needs to be ordered
      * such that more generic patterns come after more specific patterns.
      */
     private static final List<GrokPatternCandidate> ORDERED_CANDIDATE_GROK_PATTERNS = Arrays.asList(
+            new GrokPatternCandidate("TOMCAT_DATESTAMP", "timestamp"),
             new GrokPatternCandidate("TIMESTAMP_ISO8601", "timestamp"),
             new GrokPatternCandidate("DATESTAMP_RFC822", "timestamp"),
             new GrokPatternCandidate("DATESTAMP_RFC2822", "timestamp"),
@@ -41,7 +42,6 @@ public final class GrokPatternCreator {
             new GrokPatternCandidate("SYSLOGTIMESTAMP", "timestamp"),
             new GrokPatternCandidate("HTTPDATE", "timestamp"),
             new GrokPatternCandidate("CATALINA_DATESTAMP", "timestamp"),
-            new GrokPatternCandidate("TOMCAT_DATESTAMP", "timestamp"),
             new GrokPatternCandidate("CISCOTIMESTAMP", "timestamp"),
             new GrokPatternCandidate("DATE", "date"),
             new GrokPatternCandidate("TIME", "time"),
@@ -56,12 +56,10 @@ public final class GrokPatternCreator {
             new GrokPatternCandidate("IP", "ipaddress"),
             // This already includes pre/post break conditions
             new GrokPatternCandidate("QUOTEDSTRING", "field", "", ""),
-            // Can't use \b as the break before, because it doesn't work for negative numbers (the
-            // minus sign is not a "word" character)
-            new GrokPatternCandidate("NUMBER", "field", "(?<!\\w)"),
-            // Disallow +, - and . before hex numbers, otherwise this pattern will pick up base 10
-            // numbers that NUMBER rejected due to preceeding characters
-            new GrokPatternCandidate("BASE16NUM", "field", "(?<![\\w.+-])")
+            // Disallow +, - and . before numbers, as well as "word" characters, otherwise we'll pick
+            // up numeric suffices too eagerly
+            new GrokPatternCandidate("NUMBER", "field", "(?<![\\w.+-])", "(?![\\w+-]|\\.\\d)"),
+            new GrokPatternCandidate("BASE16NUM", "field", "(?<![\\w.+-])", "(?![\\w+-]|\\.\\w)")
             // TODO: also unfortunately can't have USERNAME in the list as it matches too broadly
             // Fixing these problems with overly broad matches would require some extra intelligence
             // to be added to remove inappropriate matches.  One idea would be to use a dictionary,
diff --git a/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreatorTests.java b/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreatorTests.java
index 4189dc35f0c..381a02e4580 100644
--- a/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreatorTests.java
+++ b/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/job/categorization/GrokPatternCreatorTests.java
@@ -76,6 +76,40 @@ public class GrokPatternCreatorTests extends ESTestCase {
         assertEquals(".+?%{TIMESTAMP_ISO8601:timestamp}.+?%{LOGLEVEL:loglevel}.+?", overallGrokPatternBuilder.toString());
     }
 
+    public void testAppendBestGrokMatchForStringsGivenTomcatDatestamps() {
+
+        // The first part of the Tomcat datestamp can match as an ISO8601
+        // timestamp if the ordering of candidate patterns is wrong
+        Collection<String> mustMatchStrings = Arrays.asList("2018-09-03 17:03:28,269 +0100 | ERROR | ",
+                "2018-09-03 17:04:27,279 +0100 | DEBUG | ",
+                "2018-09-03 17:05:26,289 +0100 | ERROR | ");
+
+        Map<String, Integer> fieldNameCountStore = new HashMap<>();
+        StringBuilder overallGrokPatternBuilder = new StringBuilder();
+
+        GrokPatternCreator.appendBestGrokMatchForStrings(fieldNameCountStore, overallGrokPatternBuilder, false, false, mustMatchStrings);
+
+        assertEquals(".*?%{TOMCAT_DATESTAMP:timestamp}.+?%{LOGLEVEL:loglevel}.+?", overallGrokPatternBuilder.toString());
+    }
+
+    public void testAppendBestGrokMatchForStringsGivenTrappyFloatCandidates() {
+
+        // If we're not careful then we might detect the first part of these strings as a
+        // number, e.g. 1.2 in the first example, but this is inappropriate given the
+        // trailing dot and digit
+        Collection<String> mustMatchStrings = Arrays.asList("1.2.3",
+                "-2.3.4",
+                "4.5.6.7",
+                "-9.8.7.6.5");
+
+        Map<String, Integer> fieldNameCountStore = new HashMap<>();
+        StringBuilder overallGrokPatternBuilder = new StringBuilder();
+
+        GrokPatternCreator.appendBestGrokMatchForStrings(fieldNameCountStore, overallGrokPatternBuilder, false, false, mustMatchStrings);
+
+        assertEquals(".+?", overallGrokPatternBuilder.toString());
+    }
+
     public void testAppendBestGrokMatchForStringsGivenNumbersInBrackets() {
 
         Collection<String> mustMatchStrings = Arrays.asList("(-2)",