diff --git a/runtime/syntax/sml.vim b/runtime/syntax/sml.vim
index 288b2f8c79f232..210c9fb759f012 100644
--- a/runtime/syntax/sml.vim
+++ b/runtime/syntax/sml.vim
@@ -3,7 +3,8 @@
 " Filenames:    *.sml *.sig
 " Maintainer:   Markus Mottl <markus.mottl@gmail.com>
 " Previous Maintainer: Fabrizio Zeno Cornelli <zeno@filibusta.crema.unimi.it> (invalid)
-" Last Change:  2025 Nov 07 - Update Number Regex
+" Last Change:  2025 Nov 11 - Improve special constant matching (Doug Kearns)
+" 		2025 Nov 07 - Update Number Regex
 "               2022 Apr 01
 "               2015 Aug 31 - Fixed opening of modules (Ramana Kumar)
 "               2006 Oct 23 - Fixed character highlighting bug (MM)
@@ -137,9 +138,25 @@ syn match    smlConstructor  "\u\(\w\|'\)*\>"
 " Module prefix
 syn match    smlModPath      "\u\(\w\|'\)*\."he=e-1
 
-syn match    smlCharacter    +#"\\""\|#"."\|#"\\\d\d\d"+
-syn match    smlCharErr      +#"\\\d\d"\|#"\\\d"+
-syn region   smlString       start=+"+ skip=+\\\\\|\\"+ end=+"+ contains=@Spell
+" Strings and Characters
+syn match    smlEscapeErr    "\\."                 contained
+syn match    smlEscape       "\\[abtnvfr"\\]"      contained
+syn match    smlEscapeErr    "\\^."                contained
+syn match    smlEscape       "\\^[@A-Z[\\\]^_]"    contained
+syn match    smlEscapeErr    "\\\d\{1,2}"          contained
+syn match    smlEscape       "\\\d\{3}"            contained
+syn match    smlEscapeErr    "\\u\x\{0,3}"         contained
+syn match    smlEscape       "\\u\x\{4}"           contained
+syn match    smlEscape       "\\\_[[:space:]]\+\\" contained
+syn cluster  smlEscape       contains=smlEscape,smlEscapeErr
+
+syn region   smlString       start=+"+ end=+"+ contains=@smlEscape,@Spell
+
+syn match    smlCharacter    +#"[^\\"]"+
+syn match    smlCharacter    +#"\\."+       contains=@smlEscape
+syn match    smlCharacter    +#"\\^."+      contains=@smlEscape
+syn match    smlCharacter    +#"\\\d\{3}"+  contains=@smlEscape
+syn match    smlCharacter    +#"\\u\x\{4}"+ contains=@smlEscape
 
 syn match    smlFunDef       "=>"
 syn match    smlRefAssign    ":="
@@ -156,7 +173,8 @@ syn match    smlNumber        "\~\=\<\d\+\>"
 syn match    smlNumber        "\~\=\<0x\x\+\>"
 syn match    smlWord          "\<0w\d\+\>"
 syn match    smlWord          "\<0wx\x\+\>"
-syn match    smlReal          "\~\=\<\d\+\.\d\+\%([eE]\~\=\d\+\)\=\>"
+syn match    smlReal          "\~\=\<\d\+\.\d\+\>"
+syn match    smlReal          "\~\=\<\d\+\%(\.\d\+\)\=[eE]\~\=\d\+\>"
 
 " Synchronization
 syn sync minlines=20
@@ -181,7 +199,7 @@ hi def link smlCommentErr   Error
 hi def link smlEndErr       Error
 hi def link smlThenErr      Error
 
-hi def link smlCharErr      Error
+hi def link smlEscapeErr    Error
 
 hi def link smlComment      Comment
 
@@ -213,6 +231,7 @@ hi def link smlNumber       Number
 hi def link smlWord         Number
 hi def link smlReal         Float
 hi def link smlString       String
+hi def link smlEscape       Special
 hi def link smlType         Type
 hi def link smlTodo         Todo
 hi def link smlEncl         Keyword
diff --git a/runtime/syntax/testdir/dumps/sml_00.dump b/runtime/syntax/testdir/dumps/sml_00.dump
new file mode 100644
index 00000000000000..0cd2ed21f084d6
--- /dev/null
+++ b/runtime/syntax/testdir/dumps/sml_00.dump
@@ -0,0 +1,20 @@
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diff --git a/runtime/syntax/testdir/dumps/sml_01.dump b/runtime/syntax/testdir/dumps/sml_01.dump
new file mode 100644
index 00000000000000..ad993264a86738
--- /dev/null
+++ b/runtime/syntax/testdir/dumps/sml_01.dump
@@ -0,0 +1,20 @@
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diff --git a/runtime/syntax/testdir/dumps/sml_02.dump b/runtime/syntax/testdir/dumps/sml_02.dump
new file mode 100644
index 00000000000000..d0e873e17c2768
--- /dev/null
+++ b/runtime/syntax/testdir/dumps/sml_02.dump
@@ -0,0 +1,20 @@
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diff --git a/runtime/syntax/testdir/dumps/sml_03.dump b/runtime/syntax/testdir/dumps/sml_03.dump
new file mode 100644
index 00000000000000..336d0060a1bb56
--- /dev/null
+++ b/runtime/syntax/testdir/dumps/sml_03.dump
@@ -0,0 +1,20 @@
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+|v+0#af5f00255&|a|l| +0#0000000&|_+0#af5f00255&| +0#0000000&|=+0#af5f00255&| +0#0000000&|"+0#e000002&|.@2|\+0#e000e06&|^|@|.+0#e000002&@2|\+0#e000e06&|^|A|.+0#e000002&@2|\+0#e000e06&|^|K|.+0#e000002&@2|\+0#e000e06&|^|Z|.+0#e000002&@2|\+0#e000e06&|^|[|.+0#e000002&@2|\+0#e000e06&|^|\|.+0#e000002&@2|\+0#e000e06&|^|]|.+0#e000002&@2|\+0#e000e06&|^@1|.+0#e000002&@2|\+0#e000e06&|^|_|.+0#e000002&@2|"|;+0#af5f00255&| +0#0000000&@6
+|v+0#af5f00255&|a|l| +0#0000000&|_+0#af5f00255&| +0#0000000&|=+0#af5f00255&| +0#0000000&|"+0#e000002&|\+0#e000e06&|0@2|.+0#e000002&@2|\+0#e000e06&|9@2|.+0#e000002&@2|\+0#e000e06&|u|0@3|.+0#e000002&@2|\+0#e000e06&|u|F@3|.+0#e000002&@2|"|;+0#af5f00255&| +0#0000000&@31
+@57|5@1|,|1| @9|9|4|%| 
diff --git a/runtime/syntax/testdir/dumps/sml_04.dump b/runtime/syntax/testdir/dumps/sml_04.dump
new file mode 100644
index 00000000000000..53e86ef42ca362
--- /dev/null
+++ b/runtime/syntax/testdir/dumps/sml_04.dump
@@ -0,0 +1,20 @@
+|v+0#af5f00255#ffffff0|a|l| +0#0000000&|_+0#af5f00255&| +0#0000000&|=+0#af5f00255&| +0#0000000&|"+0#e000002&|\+0#e000e06&|0@2|.+0#e000002&@2|\+0#e000e06&|9@2|.+0#e000002&@2|\+0#e000e06&|u|0@3|.+0#e000002&@2|\+0#e000e06&|u|F@3|.+0#e000002&@2|"|;+0#af5f00255&| +0#0000000&@31
+|v+0#af5f00255&|a|l| +0#0000000&|_+0#af5f00255&| +0#0000000&|=+0#af5f00255&| +0#0000000&|"+0#e000002&|.@2|\+0#e000e06&| +0#0000000&@61
+| +0#e000e06&@11|\|.+0#e000002&@2|"|;+0#af5f00255&| +0#0000000&@56
+> @74
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|7|1|,|0|-|1| @7|B|o|t| 
diff --git a/runtime/syntax/testdir/input/sml.sml b/runtime/syntax/testdir/input/sml.sml
new file mode 100644
index 00000000000000..dab0b82b920137
--- /dev/null
+++ b/runtime/syntax/testdir/input/sml.sml
@@ -0,0 +1,71 @@
+(* Integer constants *)
+
+val _ = 0;
+val _ = 42;
+val _ = 0x2A;
+val _ = ~42;         (* single token *)
+val _ = ~0x2A;       (* single token *)
+
+
+(* Word constants *)
+
+val _ = 0w0;
+val _ = 0w42;
+val _ = 0wx2A;
+val _ = ~0w42;       (* nonfix ~ *)
+val _ = ~0wx2A;      (* nonfix ~ *)
+
+
+(* Real constants *)
+
+val _ = 0.0;
+val _ = 42.42;
+val _ = 42E42;
+val _ = 42E~42;
+val _ = 42.42E42;
+val _ = 42.42E~42;
+val _ = ~42.42;      (* single token *)
+val _ = ~42.42;      (* single token *)
+val _ = ~42E42;      (* single token *)
+val _ = ~42E~42;     (* single token *)
+val _ = ~42.42E42;   (* single token *)
+val _ = ~42.42E~42;  (* single token *)
+
+
+(* Character constants *)
+
+val _ = #"a";
+val _ = #"\a";
+val _ = #"\b";
+val _ = #"\t";
+val _ = #"\n";
+val _ = #"\v";
+val _ = #"\f";
+val _ = #"\r";
+val _ = #"\"";
+val _ = #"\\";
+val _ = #"\^@";
+val _ = #"\^A";
+val _ = #"\^K";
+val _ = #"\^Z";
+val _ = #"\^[";
+val _ = #"\^\";
+val _ = #"\^]";
+val _ = #"\^^";
+val _ = #"\^_";
+val _ = #"\000";
+val _ = #"\999";
+val _ = #"\u0000";
+val _ = #"\uFFFF";
+
+
+(* String constants *)
+
+val _ = "";
+val _ = "abc";
+val _ = "...\a...\b...\t...\n...\v...\f...\r...\"...\\...";
+val _ = "...\^@...\^A...\^K...\^Z...\^[...\^\...\^]...\^^...\^_...";
+val _ = "\000...\999...\u0000...\uFFFF...";
+val _ = "...\
+            \...";
+