diff --git a/layout/base/nsBidiPresUtils.cpp b/layout/base/nsBidiPresUtils.cpp
index ad085edbb12f..b1215972c243 100644
--- a/layout/base/nsBidiPresUtils.cpp
+++ b/layout/base/nsBidiPresUtils.cpp
@@ -2363,6 +2363,12 @@ void nsBidiPresUtils::ProcessSimpleRun(const char16_t* aText, size_t aLength,
                                        nsBidiPositionResolve* aPosResolve,
                                        int32_t aPosResolveCount,
                                        nscoord* aWidth) {
+  if (!aLength) {
+    if (aWidth) {
+      *aWidth = 0;
+    }
+    return;
+  }
   // Get bidi class from the first (or only) character.
   uint32_t ch = aText[0];
   if (aLength > 1 && NS_IS_HIGH_SURROGATE(ch) &&