diff --git a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/NumberRuleTest.java b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/NumberRuleTest.java
index 81d1bcffec4..0fb106aeeeb 100644
--- a/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/NumberRuleTest.java
+++ b/core/org.eclipse.cdt.ui.tests/ui/org/eclipse/cdt/ui/tests/text/NumberRuleTest.java
@@ -114,6 +114,13 @@ public class NumberRuleTest extends TestCase {
 //		assertNoNumber("1e+");
 	}
 
+	public void testBug163691() {
+		assertNoNumber("+x1");
+		assertNoNumber("-z0");
+		assertNoNumber("- 0");
+		assertNoNumber("+ 9");
+	}
+
 	/**
 	 * Validate that given string is recognized as a number.
 	 * @param string
diff --git a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/NumberRule.java b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/NumberRule.java
index e6b87db22b5..c2344f25c9f 100644
--- a/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/NumberRule.java
+++ b/core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/text/NumberRule.java
@@ -55,7 +55,6 @@ public class NumberRule implements IRule
             }
             if (ch == '0') {
             	int xCh = scanner.read();
-            	++unreadCount;
             	if (xCh == 'x' || xCh == 'X') {
                 	// hexnumber starting with [+-]?0[xX]
                     do {
@@ -66,9 +65,9 @@ public class NumberRule implements IRule
             	}
             	scanner.unread();
             	// assert ch == '0';
-            } else if (!Character.isDigit((char)ch)) {
-            	ch = scanner.read();
-            	++unreadCount;
+            } else if (ch == '.') {
+                ch = scanner.read();
+                ++unreadCount;
             }
             if (Character.isDigit((char)ch)) {
             	// need at least one digit