--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -2697,32 +2697,27 @@ GetFontParentStyleContext(Element* aElem
       aError.Throw(NS_ERROR_FAILURE);
       return nullptr;
     }
     return result.forget();
   }
 
   // otherwise inherit from default (10px sans-serif)
 
-  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
-  if (!styleSet) {
-    // XXXheycam ServoStyleSets do not support resolving style from a list of
-    // rules yet.
-    NS_ERROR("stylo: cannot resolve style for canvas from a ServoStyleSet yet");
-    aError.Throw(NS_ERROR_FAILURE);
-    return nullptr;
-  }
-
   bool changed;
   RefPtr<css::Declaration> parentRule =
     CreateFontDeclaration(NS_LITERAL_STRING("10px sans-serif"),
                           aPresShell->GetDocument(), &changed);
 
   nsTArray<nsCOMPtr<nsIStyleRule>> parentRules;
   parentRules.AppendElement(parentRule);
+
+  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
+  MOZ_RELEASE_ASSERT(styleSet);
+
   RefPtr<nsStyleContext> result =
     styleSet->ResolveStyleForRules(nullptr, parentRules);
 
   if (!result) {
     aError.Throw(NS_ERROR_FAILURE);
     return nullptr;
   }
   return result.forget();
@@ -2741,25 +2736,16 @@ PropertyIsInheritOrInitial(Declaration* 
 }
 
 static already_AddRefed<nsStyleContext>
 GetFontStyleContext(Element* aElement, const nsAString& aFont,
                     nsIPresShell* aPresShell,
                     nsAString& aOutUsedFont,
                     ErrorResult& aError)
 {
-  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
-  if (!styleSet) {
-    // XXXheycam ServoStyleSets do not support resolving style from a list of
-    // rules yet.
-    NS_ERROR("stylo: cannot resolve style for canvas from a ServoStyleSet yet");
-    aError.Throw(NS_ERROR_FAILURE);
-    return nullptr;
-  }
-
   bool fontParsedSuccessfully = false;
   RefPtr<css::Declaration> decl =
     CreateFontDeclaration(aFont, aPresShell->GetDocument(),
                           &fontParsedSuccessfully);
 
   if (!fontParsedSuccessfully) {
     // We got a syntax error.  The spec says this value must be ignored.
     return nullptr;
@@ -2789,16 +2775,19 @@ GetFontStyleContext(Element* aElement, c
   MOZ_ASSERT(!aPresShell->IsDestroying(),
              "GetFontParentStyleContext should have returned an error if the presshell is being destroyed.");
 
   nsTArray<nsCOMPtr<nsIStyleRule>> rules;
   rules.AppendElement(decl);
   // add a rule to prevent text zoom from affecting the style
   rules.AppendElement(new nsDisableTextZoomStyleRule);
 
+  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
+  MOZ_RELEASE_ASSERT(styleSet);
+
   RefPtr<nsStyleContext> sc =
     styleSet->ResolveStyleForRules(parentContext, rules);
 
   // The font getter is required to be reserialized based on what we
   // parsed (including having line-height removed).  (Older drafts of
   // the spec required font sizes be converted to pixels, but that no
   // longer seems to be required.)
   decl->GetPropertyValueByID(eCSSProperty_font, aOutUsedFont);
@@ -2924,25 +2913,16 @@ CreateFilterDeclaration(const nsAString&
 }
 
 static already_AddRefed<nsStyleContext>
 ResolveFilterStyle(const nsAString& aFilterString,
                    nsIPresShell* aPresShell,
                    nsStyleContext* aParentContext,
                    ErrorResult& aError)
 {
-  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
-  if (!styleSet) {
-    // XXXheycam ServoStyleSets do not support resolving style from a list of
-    // rules yet.
-    NS_ERROR("stylo: cannot resolve style for canvas from a ServoStyleSet yet");
-    aError.Throw(NS_ERROR_FAILURE);
-    return nullptr;
-  }
-
   nsIDocument* document = aPresShell->GetDocument();
   bool filterChanged = false;
   RefPtr<css::Declaration> decl =
     CreateFilterDeclaration(aFilterString, document, &filterChanged);
 
   if (!filterChanged) {
     // Refuse to accept the filter, but do not throw an error.
     return nullptr;
@@ -2952,16 +2932,19 @@ ResolveFilterStyle(const nsAString& aFil
   // 'inherit' and 'initial'.
   if (PropertyIsInheritOrInitial(decl, eCSSProperty_filter)) {
     return nullptr;
   }
 
   nsTArray<nsCOMPtr<nsIStyleRule>> rules;
   rules.AppendElement(decl);
 
+  nsStyleSet* styleSet = aPresShell->StyleSet()->GetAsGecko();
+  MOZ_RELEASE_ASSERT(styleSet);
+
   RefPtr<nsStyleContext> sc =
     styleSet->ResolveStyleForRules(aParentContext, rules);
 
   return sc.forget();
 }
 
 static already_AddRefed<RawServoDeclarationBlock>
 CreateFilterDeclarationForServo(const nsAString& aFilter,