diff --git a/js/src/frontend/TokenStream.cpp b/js/src/frontend/TokenStream.cpp
index a02b22fc7850..9dc8c46873a5 100644
--- a/js/src/frontend/TokenStream.cpp
+++ b/js/src/frontend/TokenStream.cpp
@@ -808,17 +808,14 @@ TokenStreamSpecific<CharT, AnyCharsAccess>::computeErrorMetadata(ErrorMetadata*
         return true;
 
     // Add a line of context from this TokenStream to help with debugging.
-    return computeLineOfContext(err, offset);
+    return internalComputeLineOfContext(err, offset);
 }
 
 template<typename CharT, class AnyCharsAccess>
 bool
-TokenStreamSpecific<CharT, AnyCharsAccess>::computeLineOfContext(ErrorMetadata* err,
-                                                                 uint32_t offset)
+GeneralTokenStreamChars<CharT, AnyCharsAccess>::internalComputeLineOfContext(ErrorMetadata* err,
+                                                                             uint32_t offset)
 {
-    // This function presumes |err| is filled in *except* for line-of-context
-    // fields.  It exists to make |TokenStreamSpecific::computeErrorMetadata|,
-    // above, more readable.
     TokenStreamAnyChars& anyChars = anyCharsAccess();
 
     // We only have line-start information for the current line.  If the error
@@ -842,8 +839,8 @@ TokenStreamSpecific<CharT, AnyCharsAccess>::computeLineOfContext(ErrorMetadata*
     if (windowStart < this->sourceUnits.startOffset())
         windowStart = this->sourceUnits.startOffset();
 
-    // The window must end within the current line, no later than
-    // windowRadius after offset.
+    // The window must end no further than |windowRadius| after |offset| within
+    // the current line.
     size_t windowEnd = this->sourceUnits.findEOLMax(offset, windowRadius);
     size_t windowLength = windowEnd - windowStart;
     MOZ_ASSERT(windowLength <= windowRadius * 2);
@@ -851,7 +848,7 @@ TokenStreamSpecific<CharT, AnyCharsAccess>::computeLineOfContext(ErrorMetadata*
     // Create the windowed string, not including the potential line
     // terminator.
     StringBuffer windowBuf(anyChars.cx);
-    if (!windowBuf.append(codeUnitPtrAt(windowStart), windowLength) ||
+    if (!windowBuf.append(this->sourceUnits.codeUnitPtrAt(windowStart), windowLength) ||
         !windowBuf.append('\0'))
     {
         return false;
diff --git a/js/src/frontend/TokenStream.h b/js/src/frontend/TokenStream.h
index 4d0c0123ec36..d576244a74fc 100644
--- a/js/src/frontend/TokenStream.h
+++ b/js/src/frontend/TokenStream.h
@@ -1555,6 +1555,16 @@ class GeneralTokenStreamChars
     uint32_t matchUnicodeEscapeIdStart(uint32_t* codePoint);
     bool matchUnicodeEscapeIdent(uint32_t* codePoint);
 
+    /**
+     * Compute a line of context for an otherwise-filled-in |err| at the given
+     * offset in this token stream.
+     *
+     * This function is very-internal: almost certainly you should use one of
+     * its callers instead.  It basically exists only to make those callers
+     * more readable.
+     */
+    MOZ_MUST_USE bool internalComputeLineOfContext(ErrorMetadata* err, uint32_t offset);
+
   public:
     JSAtom* getRawTemplateStringAtom() {
         TokenStreamAnyChars& anyChars = anyCharsAccess();
@@ -1822,6 +1832,7 @@ class MOZ_STACK_CLASS TokenStreamSpecific
     using SpecializedChars::getFullAsciiCodePoint;
     using SpecializedChars::getNonAsciiCodePoint;
     using SpecializedChars::getNonAsciiCodePointDontNormalize;
+    using GeneralCharsBase::internalComputeLineOfContext;
     using TokenStreamCharsShared::isAsciiCodePoint;
     using CharsBase::matchCodeUnit;
     using CharsBase::matchLineTerminator;
@@ -1902,12 +1913,6 @@ class MOZ_STACK_CLASS TokenStreamSpecific
     // Warn at the current offset.
     MOZ_MUST_USE bool warning(unsigned errorNumber, ...);
 
-  private:
-    // Compute a line of context for an otherwise-filled-in |err| at the given
-    // offset in this token stream.  (This function basically exists to make
-    // |computeErrorMetadata| more readable and shouldn't be called elsewhere.)
-    MOZ_MUST_USE bool computeLineOfContext(ErrorMetadata* err, uint32_t offset);
-
   public:
     // Compute error metadata for an error at the given offset.
     MOZ_MUST_USE bool computeErrorMetadata(ErrorMetadata* err, uint32_t offset);