diff --git a/DEPS b/DEPS
index f265f12..eebc457 100644
--- a/DEPS
+++ b/DEPS
@@ -89,7 +89,7 @@
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling pdfium_tests
   # and whatever else without interference from each other.
-  'pdfium_tests_revision': 'db1faf0ee5ab4e8be140dc1c0fc0031ab70a817c',
+  'pdfium_tests_revision': '7adedee8c61163fb68005fdbd968f16532bb04d4',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling skia
   # and whatever else without interference from each other.
diff --git a/core/fxge/cfx_renderdevice.cpp b/core/fxge/cfx_renderdevice.cpp
index 7130649..dcba015 100644
--- a/core/fxge/cfx_renderdevice.cpp
+++ b/core/fxge/cfx_renderdevice.cpp
@@ -30,6 +30,7 @@
 #include "core/fxge/text_char_pos.h"
 #include "core/fxge/text_glyph_pos.h"
 #include "third_party/base/check.h"
+#include "third_party/base/check_op.h"
 #include "third_party/base/notreached.h"
 #include "third_party/base/span.h"
 
@@ -332,6 +333,11 @@
     return false;
   }
 
+  // A special case that all points are identical, zero area is formed and no
+  // thin line needs to be drawn.
+  if (points[0].m_Point == points[1].m_Point)
+    return true;
+
   for (size_t i = 0; i < 2; i++) {
     CFX_PointF point = points[i].m_Point;
     if (adjust) {
@@ -425,22 +431,21 @@
   if (CheckPalindromicPath(points, new_path, thin))
     return true;
 
-  int start_point = 0;
   for (size_t i = 0; i < points.size(); i++) {
     FXPT_TYPE point_type = points[i].m_Type;
     if (point_type == FXPT_TYPE::MoveTo) {
-      start_point = i;
+      DCHECK_EQ(0, i);
       continue;
     }
 
     if (point_type == FXPT_TYPE::BezierTo) {
       i += 2;
+      DCHECK(i < points.size());
       continue;
     }
 
     DCHECK(point_type == FXPT_TYPE::LineTo);
-    int next_index =
-        (i + 1 - start_point) % (points.size() - start_point) + start_point;
+    int next_index = (i + 1) % (points.size());
     const FX_PATHPOINT& next = points[next_index];
     if (next.m_Type == FXPT_TYPE::BezierTo || next.m_Type == FXPT_TYPE::MoveTo)
       continue;
@@ -691,12 +696,39 @@
         return true;
     }
   }
+
   if (fill && stroke_alpha == 0 && !fill_options.stroke &&
       !fill_options.text_mode) {
-    // TODO(crbug.com/pdfium/1638): Make DrawZeroAreaPath() only process a sub
-    // path instead the whole path.
-    DrawZeroAreaPath(pPathData->GetPoints(), pObject2Device,
-                     !!m_pDeviceDriver->GetDriverType(),
+    bool adjust = !!m_pDeviceDriver->GetDriverType();
+    std::vector<FX_PATHPOINT> sub_path;
+    for (size_t i = 0; i < points.size(); i++) {
+      FXPT_TYPE point_type = points[i].m_Type;
+      if (point_type == FXPT_TYPE::MoveTo) {
+        // Process the exisitng sub path.
+        DrawZeroAreaPath(sub_path, pObject2Device, adjust,
+                         fill_options.aliased_path, fill_color, fill_alpha,
+                         blend_type);
+        sub_path.clear();
+
+        // Start forming the next sub path.
+        sub_path.push_back(points[i]);
+        continue;
+      }
+
+      if (point_type == FXPT_TYPE::BezierTo) {
+        sub_path.push_back(points[i]);
+        sub_path.push_back(points[i + 1]);
+        sub_path.push_back(points[i + 2]);
+        i += 2;
+        continue;
+      }
+
+      DCHECK(point_type == FXPT_TYPE::LineTo);
+      sub_path.push_back(points[i]);
+      continue;
+    }
+    // Process the last sub paths.
+    DrawZeroAreaPath(sub_path, pObject2Device, adjust,
                      fill_options.aliased_path, fill_color, fill_alpha,
                      blend_type);
   }
diff --git a/testing/resources/pixel/bug_1638.in b/testing/resources/pixel/bug_1638.in
new file mode 100644
index 0000000..f6dea38
--- /dev/null
+++ b/testing/resources/pixel/bug_1638.in
@@ -0,0 +1,57 @@
+{{header}}
+{{object 1 0}} <<
+  /Type /Catalog
+  /Pages 2 0 R
+>>
+endobj
+{{object 2 0}} <<
+  /Type /Pages
+  /Count 1
+  /Kids [3 0 R]
+>>
+endobj
+{{object 3 0}} <<
+  /Type /Page
+  /Parent 2 0 R
+  /Contents 4 0 R
+  /MediaBox [0 0 400 400]
+  /Resources <<
+    /ExtGState <<
+      /GS1 <<
+        /ca 1.0
+      >>
+    >>
+  >>
+>>
+endobj
+{{object 4 0}} <<
+  {{streamlen}}
+>>
+stream
+q
+/GS1 gs
+0 0 1 rg
+% The 1st sub path.
+50 350 m
+200 320 l
+50 350 l
+% The 2nd sub path.
+100 300 m
+50 300 l
+200 300 l
+300 200 l
+270 230 l
+% The 3rd sub path.
+200 50 m
+350 50 l
+200 50 l
+200 100 l
+200 50 l
+f
+Q
+endstream
+endobj
+{{xref}}
+{{trailer}}
+{{startxref}}
+%%EOF
diff --git a/testing/resources/pixel/bug_1638_expected.pdf.0.png b/testing/resources/pixel/bug_1638_expected.pdf.0.png
new file mode 100644
index 0000000..23a39d5
--- /dev/null
+++ b/testing/resources/pixel/bug_1638_expected.pdf.0.png
Binary files differ