diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 35f4168e1ef9..09b8e61e7712 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,21 @@
+2017-10-26  Carlos Garcia Campos  <cgarcia@igalia.com>
+
+        REGRESSION(r222090): [HarfBuzz] Arabic shaping is broken except for first word in line
+        https://bugs.webkit.org/show_bug.cgi?id=178625
+
+        Reviewed by Michael Catanzaro.
+
+        Once we find the first space, which has the COMMON script, we split the run, and the next ones keep using
+        COMMON instead of ARABIC because we don't update the current script on every loop iteration. This patch
+        simplifies the script handling by moving the code back to the loop and always breaking in case of different
+        scripts, correctly handling INHERITED and COMMON cases and updating the current script when needed.
+
+        Covered by existing tests. This improves several tests that have been rebaselined.
+
+        * platform/graphics/harfbuzz/ComplexTextControllerHarfBuzz.cpp:
+        (WebCore::findNextRun):
+        (WebCore::scriptsAreCompatibleForCharacters): Deleted.
+
 2017-10-17  Carlos Garcia Campos  <cgarcia@igalia.com>
 
         [GTK][Stable] BackingStoreBackendCairoImpl.h:23:10: fatal error: WebCore/HysteresisActivity.h
diff --git a/Source/WebCore/platform/graphics/harfbuzz/HarfBuzzShaper.cpp b/Source/WebCore/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
index 5736903e1909..b256f7858b66 100644
--- a/Source/WebCore/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
+++ b/Source/WebCore/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
@@ -364,33 +364,6 @@ FloatPoint HarfBuzzShaper::adjustStartPoint(const FloatPoint& point)
     return point + m_startOffset;
 }
 
-static bool scriptsAreCompatibleForCharacters(UScriptCode script, UScriptCode previousScript, UChar32 character, UChar32 previousCharacter)
-{
-    if (script == previousScript)
-        return true;
-
-    if (script == USCRIPT_INHERITED || previousScript == USCRIPT_COMMON)
-        return true;
-
-    if (script == USCRIPT_COMMON) {
-        // §5.1 Handling Characters with the Common Script Property.
-        // Programs must resolve any of the special Script property values, such as Common,
-        // based on the context of the surrounding characters. A simple heuristic uses the
-        // script of the preceding character, which works well in many cases.
-        // http://www.unicode.org/reports/tr24/#Common.
-        //
-        // FIXME: cover all other cases mentioned in the spec (ie. brackets or quotation marks).
-        // https://bugs.webkit.org/show_bug.cgi?id=177003.
-        //
-        // We use a slightly more conservative heuristic than the one proposed in the spec,
-        // using the script of the previous character only if both are ASCII.
-        if (isASCII(character) && isASCII(previousCharacter))
-            return true;
-    }
-
-    return uscript_hasScript(character, previousScript);
-}
-
 bool HarfBuzzShaper::collectHarfBuzzRuns()
 {
     const UChar* normalizedBufferEnd = m_normalizedBuffer.get() + m_normalizedBufferLength;
@@ -413,7 +386,6 @@ bool HarfBuzzShaper::collectHarfBuzzRuns()
         if (!currentFontData)
             currentFontData = &m_font->primaryFont();
         UScriptCode currentScript = nextScript;
-        UChar32 previousCharacter = character;
 
         for (iterator.advance(clusterLength); iterator.consume(character, clusterLength); iterator.advance(clusterLength)) {
             if (FontCascade::treatAsZeroWidthSpace(character))
@@ -447,14 +419,31 @@ bool HarfBuzzShaper::collectHarfBuzzRuns()
             if (nextFontData != currentFontData)
                 break;
 
-            if (!scriptsAreCompatibleForCharacters(nextScript, currentScript, character, previousCharacter))
-                break;
+            // §5.1 Handling Characters with the Common Script Property.
+            // Programs must resolve any of the special Script property values, such as Common,
+            // based on the context of the surrounding characters. A simple heuristic uses the
+            // script of the preceding character, which works well in many cases.
+            // http://www.unicode.org/reports/tr24/#Common.
+            //
+            // FIXME: cover all other cases mentioned in the spec (ie. brackets or quotation marks).
+            // https://bugs.webkit.org/show_bug.cgi?id=177003.
+            //
+            // If next script is inherited or common, keep using the current script.
+            if (nextScript == USCRIPT_INHERITED || nextScript == USCRIPT_COMMON) {
+                currentCharacterPosition = iterator.characters();
+                continue;
+            }
+            // If current script is inherited or common, set the next script as current.
+            if (currentScript == USCRIPT_INHERITED || currentScript == USCRIPT_COMMON) {
+                currentScript = nextScript;
+                currentCharacterPosition = iterator.characters();
+                continue;
+            }
 
-            if (nextScript == USCRIPT_INHERITED || nextScript == USCRIPT_COMMON)
-                nextScript = currentScript;
+            if (currentScript != nextScript && !uscript_hasScript(character, currentScript))
+                break;
 
             currentCharacterPosition = iterator.characters();
-            previousCharacter = character;
         }
         unsigned numCharactersOfCurrentRun = iterator.currentIndex() - startIndexOfCurrentRun;
         hb_script_t script = hb_icu_script_to_script(currentScript);