diff --git a/mozilla/layout/generic/nsBlockBandData.cpp b/mozilla/layout/generic/nsBlockBandData.cpp
index 354786ed6ed..79b96f61349 100644
--- a/mozilla/layout/generic/nsBlockBandData.cpp
+++ b/mozilla/layout/generic/nsBlockBandData.cpp
@@ -28,7 +28,7 @@ nsBlockBandData::nsBlockBandData()
     mSpaceManagerY(0),
     mSpace(0, 0)
 {
-  mSize = 12;
+  mSize = NS_BLOCK_BAND_DATA_TRAPS;
   mTrapezoids = mData;
 }
 
diff --git a/mozilla/layout/generic/nsBlockBandData.h b/mozilla/layout/generic/nsBlockBandData.h
index c04400459f2..c287f0e632c 100644
--- a/mozilla/layout/generic/nsBlockBandData.h
+++ b/mozilla/layout/generic/nsBlockBandData.h
@@ -21,6 +21,9 @@
 
 #include "nsISpaceManager.h"
 
+// Number of builtin nsBandTrapezoid's
+#define NS_BLOCK_BAND_DATA_TRAPS 6
+
 /**
  * Class used to manage processing of the space-manager band data.
  * Provides HTML/CSS specific behavior to the raw data.
@@ -71,7 +74,7 @@ protected:
   nsSize mSpace;
 
   // Trapezoids used during band processing
-  nsBandTrapezoid mData[12];
+  nsBandTrapezoid mData[NS_BLOCK_BAND_DATA_TRAPS];
 
   // Bounding rect of available space between any left and right floaters
   nsRect mAvailSpace;
diff --git a/mozilla/layout/html/base/src/nsBlockBandData.cpp b/mozilla/layout/html/base/src/nsBlockBandData.cpp
index 354786ed6ed..79b96f61349 100644
--- a/mozilla/layout/html/base/src/nsBlockBandData.cpp
+++ b/mozilla/layout/html/base/src/nsBlockBandData.cpp
@@ -28,7 +28,7 @@ nsBlockBandData::nsBlockBandData()
     mSpaceManagerY(0),
     mSpace(0, 0)
 {
-  mSize = 12;
+  mSize = NS_BLOCK_BAND_DATA_TRAPS;
   mTrapezoids = mData;
 }
 
diff --git a/mozilla/layout/html/base/src/nsBlockBandData.h b/mozilla/layout/html/base/src/nsBlockBandData.h
index c04400459f2..c287f0e632c 100644
--- a/mozilla/layout/html/base/src/nsBlockBandData.h
+++ b/mozilla/layout/html/base/src/nsBlockBandData.h
@@ -21,6 +21,9 @@
 
 #include "nsISpaceManager.h"
 
+// Number of builtin nsBandTrapezoid's
+#define NS_BLOCK_BAND_DATA_TRAPS 6
+
 /**
  * Class used to manage processing of the space-manager band data.
  * Provides HTML/CSS specific behavior to the raw data.
@@ -71,7 +74,7 @@ protected:
   nsSize mSpace;
 
   // Trapezoids used during band processing
-  nsBandTrapezoid mData[12];
+  nsBandTrapezoid mData[NS_BLOCK_BAND_DATA_TRAPS];
 
   // Bounding rect of available space between any left and right floaters
   nsRect mAvailSpace;