diff --git a/content/html/style/src/nsCSSParser.cpp b/content/html/style/src/nsCSSParser.cpp
index 24ef2290153..f97cbc4d374 100644
--- a/content/html/style/src/nsCSSParser.cpp
+++ b/content/html/style/src/nsCSSParser.cpp
@@ -5197,7 +5197,9 @@ PRBool CSSParserImpl::ParseFont(nsresult& aErrorCode)
   // Get optional "/" line-height
   nsCSSValue  lineHeight;
   if (ExpectSymbol(aErrorCode, '/', PR_TRUE)) {
-    if (! ParseVariant(aErrorCode, lineHeight, VARIANT_NUMBER | VARIANT_LP | VARIANT_NORMAL, nsnull)) {
+    if (! ParsePositiveVariant(aErrorCode, lineHeight,
+                               VARIANT_NUMBER | VARIANT_LP | VARIANT_NORMAL,
+                               nsnull)) {
       return PR_FALSE;
     }
   }
diff --git a/layout/generic/nsHTMLReflowState.cpp b/layout/generic/nsHTMLReflowState.cpp
index 55bb6004d77..71d09568439 100644
--- a/layout/generic/nsHTMLReflowState.cpp
+++ b/layout/generic/nsHTMLReflowState.cpp
@@ -2185,27 +2185,14 @@ nsHTMLReflowState::CalcLineHeight(nsIPresContext* aPresContext,
                                   nsIRenderingContext* aRenderingContext,
                                   nsIFrame* aFrame)
 {
-  nscoord lineHeight = -1;
-  nsStyleContext* sc = aFrame->GetStyleContext();
-  if (sc) {
-    lineHeight = ComputeLineHeight(aPresContext, aRenderingContext, sc);
-  }
-  if (lineHeight < 0) {
-    // Negative line-heights are not allowed by the spec. Translate
-    // them into "normal" when found.
-    const nsStyleFont* font = sc->GetStyleFont();
-    if (UseComputedHeight()) {
-      lineHeight = font->mFont.size;
-    }
-    else {
-      SetFontFromStyle(aRenderingContext, sc);
-      nsCOMPtr<nsIFontMetrics> fm;
-      aRenderingContext->GetFontMetrics(*getter_AddRefs(fm));
-      if (fm) {
-        lineHeight = GetNormalLineHeight(fm);
-      }
-    }
-  }
+  NS_ASSERTION(aFrame && aFrame->GetStyleContext(),
+               "Bogus data passed in to CalcLineHeight");
+
+  nscoord lineHeight = ComputeLineHeight(aPresContext, aRenderingContext,
+                                         aFrame->GetStyleContext());
+
+  NS_ASSERTION(lineHeight >= 0, "ComputeLineHeight screwed up");
+
   return lineHeight;
 }
 
diff --git a/layout/html/base/src/nsHTMLReflowState.cpp b/layout/html/base/src/nsHTMLReflowState.cpp
index 55bb6004d77..71d09568439 100644
--- a/layout/html/base/src/nsHTMLReflowState.cpp
+++ b/layout/html/base/src/nsHTMLReflowState.cpp
@@ -2185,27 +2185,14 @@ nsHTMLReflowState::CalcLineHeight(nsIPresContext* aPresContext,
                                   nsIRenderingContext* aRenderingContext,
                                   nsIFrame* aFrame)
 {
-  nscoord lineHeight = -1;
-  nsStyleContext* sc = aFrame->GetStyleContext();
-  if (sc) {
-    lineHeight = ComputeLineHeight(aPresContext, aRenderingContext, sc);
-  }
-  if (lineHeight < 0) {
-    // Negative line-heights are not allowed by the spec. Translate
-    // them into "normal" when found.
-    const nsStyleFont* font = sc->GetStyleFont();
-    if (UseComputedHeight()) {
-      lineHeight = font->mFont.size;
-    }
-    else {
-      SetFontFromStyle(aRenderingContext, sc);
-      nsCOMPtr<nsIFontMetrics> fm;
-      aRenderingContext->GetFontMetrics(*getter_AddRefs(fm));
-      if (fm) {
-        lineHeight = GetNormalLineHeight(fm);
-      }
-    }
-  }
+  NS_ASSERTION(aFrame && aFrame->GetStyleContext(),
+               "Bogus data passed in to CalcLineHeight");
+
+  nscoord lineHeight = ComputeLineHeight(aPresContext, aRenderingContext,
+                                         aFrame->GetStyleContext());
+
+  NS_ASSERTION(lineHeight >= 0, "ComputeLineHeight screwed up");
+
   return lineHeight;
 }
 
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 24ef2290153..f97cbc4d374 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -5197,7 +5197,9 @@ PRBool CSSParserImpl::ParseFont(nsresult& aErrorCode)
   // Get optional "/" line-height
   nsCSSValue  lineHeight;
   if (ExpectSymbol(aErrorCode, '/', PR_TRUE)) {
-    if (! ParseVariant(aErrorCode, lineHeight, VARIANT_NUMBER | VARIANT_LP | VARIANT_NORMAL, nsnull)) {
+    if (! ParsePositiveVariant(aErrorCode, lineHeight,
+                               VARIANT_NUMBER | VARIANT_LP | VARIANT_NORMAL,
+                               nsnull)) {
       return PR_FALSE;
     }
   }