diff --git a/src/java/org/apache/poi/ss/format/CellFormatPart.java b/src/java/org/apache/poi/ss/format/CellFormatPart.java
index 2c65ca865d..c03dbc5795 100644
--- a/src/java/org/apache/poi/ss/format/CellFormatPart.java
+++ b/src/java/org/apache/poi/ss/format/CellFormatPart.java
@@ -108,7 +108,7 @@ public class CellFormatPart {
     static {
         // A condition specification
         String condition = "([<>=]=?|!=|<>)    # The operator\n" +
-                "  \\s*([0-9]+(?:\\.[0-9]*)?)\\s*  # The constant to test against\n";
+                "  \\s*(-?[0-9]+(?:\\.[0-9]*)?)\\s*  # The constant to test against\n";
 
         // A currency symbol / string, in a specific locale
         String currency = "(\\[\\$.{0,3}-[0-9a-f]{3}\\])";
diff --git a/test-data/spreadsheet/FormatConditionTests.xlsx b/test-data/spreadsheet/FormatConditionTests.xlsx
index 22622586f8..432e54630a 100644
Binary files a/test-data/spreadsheet/FormatConditionTests.xlsx and b/test-data/spreadsheet/FormatConditionTests.xlsx differ