--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -8383,17 +8383,18 @@ nsTextFrame::ReflowText(nsLineLayout& aL
   uint32_t transformedLastBreak = 0;
   bool usedHyphenation;
   gfxFloat trimmedWidth = 0;
   gfxFloat availWidth = aAvailableWidth;
   bool canTrimTrailingWhitespace = !textStyle->WhiteSpaceIsSignificant() ||
                                    (GetStateBits() & TEXT_IS_IN_TOKEN_MATHML);
   gfxBreakPriority breakPriority = aLineLayout.LastOptionalBreakPriority();
   gfxTextRun::SuppressBreak suppressBreak = gfxTextRun::eNoSuppressBreak;
-  if (ShouldSuppressLineBreak()) {
+  bool shouldSuppressLineBreak = ShouldSuppressLineBreak();
+  if (shouldSuppressLineBreak) {
     suppressBreak = gfxTextRun::eSuppressAllBreaks;
   } else if (!aLineLayout.LineIsBreakable()) {
     suppressBreak = gfxTextRun::eSuppressInitialBreak;
   }
   uint32_t transformedCharsFit =
     mTextRun->BreakAndMeasureText(transformedOffset, transformedLength,
                                   (GetStateBits() & TEXT_START_OF_LINE) != 0,
                                   availWidth,
@@ -8578,46 +8579,48 @@ nsTextFrame::ReflowText(nsLineLayout& aL
   // from the last textframe should be preserved. Otherwise the trimmable width
   // from this textframe overrides. (Currently in CSS trimmable width can be
   // at most one space so there's no way for trimmable width from a previous
   // frame to accumulate with trimmable width from this frame.)
   if (transformedCharsFit > 0) {
     aLineLayout.SetTrimmableISize(NSToCoordFloor(trimmableWidth));
     AddStateBits(TEXT_HAS_NONCOLLAPSED_CHARACTERS);
   }
-  if (charsFit > 0 && charsFit == length &&
-      textStyle->mHyphens != NS_STYLE_HYPHENS_NONE &&
-      HasSoftHyphenBefore(frag, mTextRun, offset, end)) {
-    bool fits =
-      textMetrics.mAdvanceWidth + provider.GetHyphenWidth() <= availWidth;
-    // Record a potential break after final soft hyphen
-    aLineLayout.NotifyOptionalBreakPosition(this, length, fits,
-                                            gfxBreakPriority::eNormalBreak);
-  }
   bool breakAfter = forceBreakAfter;
-  // length == 0 means either the text is empty or it's all collapsed away
-  bool emptyTextAtStartOfLine = atStartOfLine && length == 0;
-  if (!breakAfter && charsFit == length && !emptyTextAtStartOfLine &&
-      transformedOffset + transformedLength == mTextRun->GetLength() &&
-      !ShouldSuppressLineBreak() &&
-      (mTextRun->GetFlags() & nsTextFrameUtils::TEXT_HAS_TRAILING_BREAK)) {
-    // We placed all the text in the textrun and we have a break opportunity at
-    // the end of the textrun. We need to record it because the following
-    // content may not care about nsLineBreaker.
-
-    // Note that because we didn't break, we can be sure that (thanks to the
-    // code up above) textMetrics.mAdvanceWidth includes the width of any
-    // trailing whitespace. So we need to subtract trimmableWidth here
-    // because if we did break at this point, that much width would be trimmed.
-    if (textMetrics.mAdvanceWidth - trimmableWidth > availWidth) {
-      breakAfter = true;
-    } else {
-      aLineLayout.NotifyOptionalBreakPosition(this, length, true,
+  if (!shouldSuppressLineBreak) {
+    if (charsFit > 0 && charsFit == length &&
+        textStyle->mHyphens != NS_STYLE_HYPHENS_NONE &&
+        HasSoftHyphenBefore(frag, mTextRun, offset, end)) {
+      bool fits =
+        textMetrics.mAdvanceWidth + provider.GetHyphenWidth() <= availWidth;
+      // Record a potential break after final soft hyphen
+      aLineLayout.NotifyOptionalBreakPosition(this, length, fits,
                                               gfxBreakPriority::eNormalBreak);
     }
+    // length == 0 means either the text is empty or it's all collapsed away
+    bool emptyTextAtStartOfLine = atStartOfLine && length == 0;
+    if (!breakAfter && charsFit == length && !emptyTextAtStartOfLine &&
+        transformedOffset + transformedLength == mTextRun->GetLength() &&
+        (mTextRun->GetFlags() & nsTextFrameUtils::TEXT_HAS_TRAILING_BREAK)) {
+      // We placed all the text in the textrun and we have a break opportunity
+      // at the end of the textrun. We need to record it because the following
+      // content may not care about nsLineBreaker.
+
+      // Note that because we didn't break, we can be sure that (thanks to the
+      // code up above) textMetrics.mAdvanceWidth includes the width of any
+      // trailing whitespace. So we need to subtract trimmableWidth here
+      // because if we did break at this point, that much width would be
+      // trimmed.
+      if (textMetrics.mAdvanceWidth - trimmableWidth > availWidth) {
+        breakAfter = true;
+      } else {
+        aLineLayout.NotifyOptionalBreakPosition(this, length, true,
+                                                gfxBreakPriority::eNormalBreak);
+      }
+    }
   }
 
   // Compute reflow status
   aStatus = contentLength == maxContentLength
     ? NS_FRAME_COMPLETE : NS_FRAME_NOT_COMPLETE;
 
   if (charsFit == 0 && length > 0 && !usedHyphenation) {
     // Couldn't place any text
@@ -8654,17 +8657,17 @@ nsTextFrame::ReflowText(nsLineLayout& aL
   } else if (cachedNewlineOffset) {
     mContent->DeleteProperty(nsGkAtoms::newline);
   }
 
   // Compute space and letter counts for justification, if required
   if (!textStyle->WhiteSpaceIsSignificant() &&
       (lineContainer->StyleText()->mTextAlign == NS_STYLE_TEXT_ALIGN_JUSTIFY ||
        lineContainer->StyleText()->mTextAlignLast == NS_STYLE_TEXT_ALIGN_JUSTIFY ||
-       ShouldSuppressLineBreak()) &&
+       shouldSuppressLineBreak) &&
       !lineContainer->IsSVGText()) {
     AddStateBits(TEXT_JUSTIFICATION_ENABLED);
     provider.ComputeJustification(offset, charsFit);
     aLineLayout.SetJustificationInfo(provider.GetJustificationInfo());
   }
 
   SetLength(contentLength, &aLineLayout, ALLOW_FRAME_CREATION_AND_DESTRUCTION);
 

new file mode 100644
--- /dev/null
+++ b/layout/reftests/css-ruby/line-break-suppression-5-ref.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <title>Bug 1186720 - Line break suppression with soft hyphen</title>
+</head>
+<body style="width: 1px">
+  x<ruby>a</ruby>
+</body>
+</html>

new file mode 100644
--- /dev/null
+++ b/layout/reftests/css-ruby/line-break-suppression-5.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <title>Bug 1186720 - Line break suppression with soft hyphen</title>
+</head>
+<body style="width: 1px">
+  x<ruby>a&shy;</ruby>
+</body>
+</html>

--- a/layout/reftests/css-ruby/reftest.list
+++ b/layout/reftests/css-ruby/reftest.list
@@ -28,16 +28,17 @@ test-pref(dom.meta-viewport.enabled,true
 == justification-2.html justification-2-ref.html
 fuzzy-if(winWidget,255,792) == lang-specific-style-1.html lang-specific-style-1-ref.html # bug 1134947
 == line-breaking-1.html line-breaking-1-ref.html
 == line-breaking-2.html line-breaking-2-ref.html
 == line-break-suppression-1.html line-break-suppression-1-ref.html
 == line-break-suppression-2.html line-break-suppression-2-ref.html
 == line-break-suppression-3.html line-break-suppression-3-ref.html
 == line-break-suppression-4.html line-break-suppression-4-ref.html
+== line-break-suppression-5.html line-break-suppression-5-ref.html
 == line-height-1.html line-height-1-ref.html
 == line-height-2.html line-height-2-ref.html
 == line-height-3.html line-height-3-ref.html
 == line-height-4.html line-height-4-ref.html
 load nested-ruby-1.html
 == no-transform.html no-transform-ref.html
 == relative-positioning-1.html relative-positioning-1-ref.html
 == relative-positioning-2.html relative-positioning-2-ref.html