diff --git a/dom/smil/SMILParserUtils.cpp b/dom/smil/SMILParserUtils.cpp
index c37d9e48db5a..87b76cbdb78b 100644
--- a/dom/smil/SMILParserUtils.cpp
+++ b/dom/smil/SMILParserUtils.cpp
@@ -165,7 +165,7 @@ bool ParseClockValue(RangedPtr<const char16_t>& aIter,
 
   iter = aIter;
 
-  int32_t hours = 0, timecount;
+  int32_t hours = 0, timecount = 0;
   double fraction = 0.0;
   uint32_t minutes, seconds, multiplier;
 
@@ -192,7 +192,8 @@ bool ParseClockValue(RangedPtr<const char16_t>& aIter,
       aIter = iter;
       return true;
     case TIMECOUNT_VALUE:
-      if (!SVGContentUtils::ParseInteger(iter, aEnd, timecount)) {
+      if (*iter != '.' &&
+          !SVGContentUtils::ParseInteger(iter, aEnd, timecount)) {
         return false;
       }
       if (iter != aEnd && *iter == '.' &&
diff --git a/dom/smil/test/test_smilGetSimpleDuration.xhtml b/dom/smil/test/test_smilGetSimpleDuration.xhtml
index a54139a89872..7726950b6332 100644
--- a/dom/smil/test/test_smilGetSimpleDuration.xhtml
+++ b/dom/smil/test/test_smilGetSimpleDuration.xhtml
@@ -33,6 +33,8 @@ function main() {
   /* Check basic operation */
   anim.setAttribute("dur", "1s");
   is(anim.getSimpleDuration(), 1);
+  anim.setAttribute("dur", ".15s");
+  isfuzzy(anim.getSimpleDuration(), 0.15, 0.001);
   anim.setAttribute("dur", "1.5s");
   is(anim.getSimpleDuration(), 1.5);
 
diff --git a/dom/smil/test/test_smilInvalidValues.html b/dom/smil/test/test_smilInvalidValues.html
index d6a262fc8d9f..f65d4d7dff9e 100644
--- a/dom/smil/test/test_smilInvalidValues.html
+++ b/dom/smil/test/test_smilInvalidValues.html
@@ -60,10 +60,14 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=941315
     a.setAttribute("dur", "50s");
     is(b.safeGetStartTime(), 50, "valid simple duration");
 
-    // Check an invalid value also causes the model to be updated
+    // Check invalid values also cause the model to be updated
     a.setAttribute("dur", "abc"); // -> indefinite
     is(b.safeGetStartTime(), "none", "invalid simple duration");
 
+    a.setAttribute("dur", "50s");
+    a.setAttribute("dur", "-.1s"); // -> indefinite
+    is(b.safeGetStartTime(), "none", "invalid simple duration");
+
     // Restore state
     a.setAttribute("dur", "100s");
   }