diff --git a/source/data/mappings/gb18030.ucm b/source/data/mappings/gb18030.ucm
index f8f0cb0..6f40ba4 100644
--- a/source/data/mappings/gb18030.ucm
+++ b/source/data/mappings/gb18030.ucm
@@ -3132,6 +3132,7 @@ CHARMAP
 <U2FFE> \x81\x39\xA3\x34 |0
 <U2FFF> \x81\x39\xA3\x35 |0
 <U3000> \xA1\xA1 |0
+<U3000> \xA3\xA0 |3
 <U3001> \xA1\xA2 |0
 <U3002> \xA1\xA3 |0
 <U3003> \xA1\xA8 |0
@@ -29584,7 +29585,6 @@ CHARMAP
 <UE5E2> \xA3\x9D |0
 <UE5E3> \xA3\x9E |0
 <UE5E4> \xA3\x9F |0
-<UE5E5> \xA3\xA0 |0
 <UE5E6> \xA4\x40 |0
 <UE5E7> \xA4\x41 |0
 <UE5E8> \xA4\x42 |0
diff --git a/source/data/mappings/windows-936-2000.ucm b/source/data/mappings/windows-936-2000.ucm
index 6cfafab..66c9a31 100644
--- a/source/data/mappings/windows-936-2000.ucm
+++ b/source/data/mappings/windows-936-2000.ucm
@@ -37,7 +37,8 @@
 
 # build an extension-only (delta) .cnv file
 # requires the base .cnv file at runtime
-<icu:base>                    "ibm-1386_P100-2001"
+# Chromium: we don't want ibm-1386
+#<icu:base>                    "ibm-1386_P100-2001"
 
 # The following was the generated state table.
 # This does not account for unassigned characters
@@ -259,6 +260,7 @@ CHARMAP
 <U01DA> \xA8\xB7 |0
 <U01DB> \xA8\xB8 |1
 <U01DC> \xA8\xB8 |0
+<U01F9> \xA8\xBF |0
 <U0251> \xA8\xBB |0
 <U0261> \xA8\xC0 |0
 <U02C7> \xA1\xA6 |0
@@ -380,6 +382,9 @@ CHARMAP
 <U044E> \xA7\xF0 |0
 <U044F> \xA7\xF1 |0
 <U0451> \xA7\xD7 |0
+# U1E3F will be round-tripped and UE7C7 will be dropped 
+# once https://www.w3.org/Bugs/Public/show_bug.cgi?id=28740#c3 is resolved.
+<U1E3F> \xA8\xBC |1
 <U2010> \xA9\x5C |0
 <U2013> \xA8\x43 |0
 <U2014> \xA1\xAA |0
@@ -23435,7 +23440,7 @@ CHARMAP
 <UE5E2> \xA3\x9D |0
 <UE5E3> \xA3\x9E |0
 <UE5E4> \xA3\x9F |0
-<UE5E5> \xA3\xA0 |0
+<U3000> \xA3\xA0 |3
 <UE5E6> \xA4\x40 |0
 <UE5E7> \xA4\x41 |0
 <UE5E8> \xA4\x42 |0
@@ -23918,7 +23923,6 @@ CHARMAP
 <UE7C5> \xA8\x9F |0
 <UE7C6> \xA8\xA0 |0
 <UE7C7> \xA8\xBC |0
-<UE7C8> \xA8\xBF |0
 <UE7C9> \xA8\xC1 |0
 <UE7CA> \xA8\xC2 |0
 <UE7CB> \xA8\xC3 |0