diff --git a/src/builtin_argparse.cpp b/src/builtin_argparse.cpp
index 1b75a40a4..b6c4405c6 100644
--- a/src/builtin_argparse.cpp
+++ b/src/builtin_argparse.cpp
@@ -181,6 +181,8 @@ static bool parse_flag_modifiers(const argparse_cmd_opts_t &opts, const option_s
     if (*s == L'!') {
         s++;
         opt_spec->validation_command = wcstring(s);
+        // Move cursor to the end so we don't expect a long flag.
+        while (*s) s++;
     } else if (*s) {
         streams.err.append_format(BUILTIN_ERR_INVALID_OPT_SPEC, opts.name.c_str(),
                                   option_spec.c_str(), *s);
diff --git a/tests/argparse.err b/tests/argparse.err
index 417c205a0..291e53221 100644
--- a/tests/argparse.err
+++ b/tests/argparse.err
@@ -121,3 +121,8 @@ in function 'notargparse'
 
 ####################
 # Checking arguments after --
+
+####################
+# Checking validation for short flags only
+argparse: Value 'banana' for flag 'o' is not an integer
+argparse: Value '-o' for flag 'i' is not an integer
diff --git a/tests/argparse.in b/tests/argparse.in
index 01d9aba3b..444501d7c 100644
--- a/tests/argparse.in
+++ b/tests/argparse.in
@@ -195,3 +195,12 @@ begin
     argparse a/alpha -- a --alpha -- b -a
     printf '%s\n' $argv
 end
+
+# #5864 - short flag only with same validation function.
+logmsg Checking validation for short flags only
+argparse 'i=!_validate_int' 'o=!_validate_int' -- -i 2 -o banana
+argparse 'i=!_validate_int' 'o=!_validate_int' -- -i -o banana
+begin
+    argparse 'i=!_validate_int' 'o=!_validate_int' -- -i 2 -o 3
+    set -l
+end
diff --git a/tests/argparse.out b/tests/argparse.out
index c70257994..130ae04aa 100644
--- a/tests/argparse.out
+++ b/tests/argparse.out
@@ -146,3 +146,15 @@ alpha aaaa
 a
 b
 -a
+
+####################
+# Checking validation for short flags only
+_flag_a 'alpha'  'aaaa'
+_flag_b -b
+_flag_break -b
+_flag_i 2
+_flag_m 1
+_flag_max 1
+_flag_o 3
+argv
+saved_status 57