diff --git a/layout/generic/nsHTMLReflowState.cpp b/layout/generic/nsHTMLReflowState.cpp
index 8eabc8ebb26..d73a33f05da 100644
--- a/layout/generic/nsHTMLReflowState.cpp
+++ b/layout/generic/nsHTMLReflowState.cpp
@@ -2290,6 +2290,10 @@ ComputeLineHeight(nsIPresContext* aPresContext,
     nsCOMPtr<nsIFontMetrics> fm;
     deviceContext->GetMetricsFor(font->mFont, langGroup, *getter_AddRefs(fm));
 
+    if (!fm) {
+      NS_WARNING( "null font metrics for the device context - we have to fix this someday...");
+    }
+
     if (unit == eStyleUnit_Factor) {
       // For factor units the computed value of the line-height property 
       // is found by multiplying the factor by the font's <b>actual</b> 
@@ -2303,7 +2307,7 @@ ComputeLineHeight(nsIPresContext* aPresContext,
       // precise layout in the face of imprecise fonts.
       nscoord emHeight = font->mFont.size;
 #ifdef NEW_FONT_HEIGHT_APIS
-      if (!nsHTMLReflowState::UseComputedHeight()) {
+      if (!nsHTMLReflowState::UseComputedHeight() && fm) {
         fm->GetEmHeight(emHeight);
       }
 #endif
@@ -2312,7 +2316,7 @@ ComputeLineHeight(nsIPresContext* aPresContext,
       NS_ASSERTION(eStyleUnit_Normal == unit, "bad unit");
       lineHeight = font->mFont.size;
 #ifdef NEW_FONT_HEIGHT_APIS
-      if (!nsHTMLReflowState::UseComputedHeight()) {
+      if (!nsHTMLReflowState::UseComputedHeight() && fm) {
         lineHeight = GetNormalLineHeight(fm);
       }
 #endif
diff --git a/layout/html/base/src/nsHTMLReflowState.cpp b/layout/html/base/src/nsHTMLReflowState.cpp
index 8eabc8ebb26..d73a33f05da 100644
--- a/layout/html/base/src/nsHTMLReflowState.cpp
+++ b/layout/html/base/src/nsHTMLReflowState.cpp
@@ -2290,6 +2290,10 @@ ComputeLineHeight(nsIPresContext* aPresContext,
     nsCOMPtr<nsIFontMetrics> fm;
     deviceContext->GetMetricsFor(font->mFont, langGroup, *getter_AddRefs(fm));
 
+    if (!fm) {
+      NS_WARNING( "null font metrics for the device context - we have to fix this someday...");
+    }
+
     if (unit == eStyleUnit_Factor) {
       // For factor units the computed value of the line-height property 
       // is found by multiplying the factor by the font's <b>actual</b> 
@@ -2303,7 +2307,7 @@ ComputeLineHeight(nsIPresContext* aPresContext,
       // precise layout in the face of imprecise fonts.
       nscoord emHeight = font->mFont.size;
 #ifdef NEW_FONT_HEIGHT_APIS
-      if (!nsHTMLReflowState::UseComputedHeight()) {
+      if (!nsHTMLReflowState::UseComputedHeight() && fm) {
         fm->GetEmHeight(emHeight);
       }
 #endif
@@ -2312,7 +2316,7 @@ ComputeLineHeight(nsIPresContext* aPresContext,
       NS_ASSERTION(eStyleUnit_Normal == unit, "bad unit");
       lineHeight = font->mFont.size;
 #ifdef NEW_FONT_HEIGHT_APIS
-      if (!nsHTMLReflowState::UseComputedHeight()) {
+      if (!nsHTMLReflowState::UseComputedHeight() && fm) {
         lineHeight = GetNormalLineHeight(fm);
       }
 #endif