diff --git a/dexter/Commands.md b/dexter/Commands.md
index 27d6993..f61418b 100644
--- a/dexter/Commands.md
+++ b/dexter/Commands.md
@@ -217,8 +217,13 @@
 
 ### Description
 Name the line this command is found on or 'on_line' if it is provided. Line
-names can be referenced by other commands expecting line number arguments.
-For example, `DexExpectWatchValues(..., on_line='my_line_name')`.
+names can be converted to line numbers with the `ref(str)` function. For
+example, `DexExpectWatchValues(..., on_line=ref('my_line_name'))`. Use
+arithmetic operators to get offsets from labels:
+
+    DexExpectWatchValues(..., on_line=ref('my_line_name') + 3)
+    DexExpectWatchValues(..., on_line=ref('my_line_name') - 5)
+
 
 ### Heuristic
 This command does not contribute to the heuristic score.
diff --git a/dexter/dex/command/ParseCommand.py b/dexter/dex/command/ParseCommand.py
index 8246ea9..c9908ef 100644
--- a/dexter/dex/command/ParseCommand.py
+++ b/dexter/dex/command/ParseCommand.py
@@ -69,7 +69,7 @@
     return valid_commands
 
 
-def _build_command(command_type, raw_text: str, path: str, lineno: str) -> CommandBase:
+def _build_command(command_type, labels, raw_text: str, path: str, lineno: str) -> CommandBase:
     """Build a command object from raw text.
 
     This function will call eval().
@@ -80,8 +80,18 @@
     Returns:
         A dexter command object.
     """
+    def label_to_line(label_name: str) -> int:
+        line = labels.get(label_name, None)
+        if line != None:
+            return line
+        raise format_unresolved_label_err(label_name, raw_text, path, lineno)
+
     valid_commands = _merge_subcommands(
-        command_type.get_name(), { command_type.get_name(): command_type })
+        command_type.get_name(), {
+            'ref': label_to_line,
+            command_type.get_name(): command_type,
+        })
+
     # pylint: disable=eval-used
     command = eval(raw_text, valid_commands)
     # pylint: enable=eval-used
@@ -91,27 +101,6 @@
     return command
 
 
-def resolve_labels(command: CommandBase, commands: dict):
-    """Attempt to resolve any labels in command"""
-    dex_labels = commands['DexLabel']
-    command_label_args = command.get_label_args()
-    for command_arg in command_label_args:
-        for dex_label in list(dex_labels.values()):
-            if (os.path.samefile(dex_label.path, command.path) and
-                dex_label.eval() == command_arg):
-                command.resolve_label(dex_label.get_as_pair())
-    # labels for command should be resolved by this point.
-    if command.has_labels():
-        syntax_error = SyntaxError()
-        syntax_error.filename = command.path
-        syntax_error.lineno = command.lineno
-        syntax_error.offset = 0
-        syntax_error.msg = 'Unresolved labels'
-        for label in command.get_label_args():
-            syntax_error.msg += ' \'' + label + '\''
-        raise syntax_error
-
-
 def _search_line_for_cmd_start(line: str, start: int, valid_commands: dict) -> int:
     """Scan `line` for a string matching any key in `valid_commands`.
 
@@ -176,6 +165,16 @@
         return self.char + 1
 
 
+def format_unresolved_label_err(label: str, src: str, filename: str, lineno) -> CommandParseError:
+    err = CommandParseError()
+    err.src = src
+    err.caret = '' # Don't bother trying to point to the bad label.
+    err.filename = filename
+    err.lineno = lineno
+    err.info = f'Unresolved label: \'{label}\''
+    return err
+
+
 def format_parse_err(msg: str, path: str, lines: list, point: TextPoint) -> CommandParseError:
     err = CommandParseError()
     err.filename = path
@@ -193,10 +192,27 @@
             return
 
 
+def add_line_label(labels, label, cmd_path, cmd_lineno):
+    # Enforce unique line labels.
+    if label.eval() in labels:
+        err = CommandParseError()
+        err.info = f'Found duplicate line label: \'{label.eval()}\''
+        err.lineno = cmd_lineno
+        err.filename = cmd_path
+        err.src = label.raw_text
+        # Don't both trying to point to it since we're only printing the raw
+        # command, which isn't much text.
+        err.caret = ''
+        raise err
+    labels[label.eval()] = label.get_line()
+
+
 def _find_all_commands_in_file(path, file_lines, valid_commands):
+    labels = {} # dict of {name: line}.
     commands = defaultdict(dict)
     paren_balance = 0
     region_start = TextPoint(0, 0)
+
     for region_start.line in range(len(file_lines)):
         line = file_lines[region_start.line]
         region_start.char = 0
@@ -222,7 +238,7 @@
             end, paren_balance = _search_line_for_cmd_end(line, region_start.char, paren_balance)
             # Add this text blob to the command.
             cmd_text_list.append(line[region_start.char:end])
-            # Move parse ptr to end of line or parens
+            # Move parse ptr to end of line or parens.
             region_start.char = end
 
             # If the parens are unbalanced start reading the next line in an attempt
@@ -235,6 +251,7 @@
             try:
                 command = _build_command(
                     valid_commands[command_name],
+                    labels,
                     raw_text,
                     path,
                     cmd_point.get_lineno(),
@@ -252,7 +269,8 @@
                 err_point.char += len(command_name)
                 raise format_parse_err(str(e), path, file_lines, err_point)
             else:
-                resolve_labels(command, commands)
+                if type(command) is DexLabel:
+                    add_line_label(labels, command, path, cmd_point.get_lineno())
                 assert (path, cmd_point) not in commands[command_name], (
                     command_name, commands[command_name])
                 commands[command_name][path, cmd_point] = command
diff --git a/dexter/dex/command/commands/DexExpectProgramState.py b/dexter/dex/command/commands/DexExpectProgramState.py
index 7833583..26f97b6 100644
--- a/dexter/dex/command/commands/DexExpectProgramState.py
+++ b/dexter/dex/command/commands/DexExpectProgramState.py
@@ -66,18 +66,3 @@
                 self.encounters.append(step.step_index)
 
         return self.times < 0 < len(self.encounters) or len(self.encounters) == self.times
-
-    def has_labels(self):
-        return len(self.get_label_args()) > 0
-
-    def get_label_args(self):
-        return [frame.location.lineno
-                    for frame in self.expected_program_state.frames
-                        if frame.location and
-                        isinstance(frame.location.lineno, str)]
-
-    def resolve_label(self, label_line__pair):
-        label, line = label_line__pair
-        for frame in self.expected_program_state.frames:
-            if frame.location and frame.location.lineno == label:
-                frame.location.lineno = line
diff --git a/dexter/dex/command/commands/DexExpectWatchBase.py b/dexter/dex/command/commands/DexExpectWatchBase.py
index 24ef4cc..e892f01 100644
--- a/dexter/dex/command/commands/DexExpectWatchBase.py
+++ b/dexter/dex/command/commands/DexExpectWatchBase.py
@@ -82,22 +82,6 @@
     def encountered_values(self):
         return sorted(list(set(self.values) - self._missing_values))
 
-
-    def resolve_label(self, label_line_pair):
-        # from_line and to_line could have the same label.
-        label, lineno = label_line_pair
-        if self._to_line == label:
-            self._to_line = lineno
-        if self._from_line == label:
-            self._from_line = lineno
-
-    def has_labels(self):
-        return len(self.get_label_args()) > 0
-
-    def get_label_args(self):
-        return [label for label in (self._from_line, self._to_line)
-                      if isinstance(label, str)]
-
     @abc.abstractmethod
     def _get_expected_field(self, watch):
         """Return a field from watch that this ExpectWatch command is checking.
diff --git a/dexter/dex/command/commands/DexLimitSteps.py b/dexter/dex/command/commands/DexLimitSteps.py
index 09eb050..5090ff4 100644
--- a/dexter/dex/command/commands/DexLimitSteps.py
+++ b/dexter/dex/command/commands/DexLimitSteps.py
@@ -32,22 +32,6 @@
                 ', '.join(kwargs)))
         super(DexLimitSteps, self).__init__()
 
-    def resolve_label(self, label_line_pair):
-        label, lineno = label_line_pair
-        if isinstance(self.from_line, str):
-            if self.from_line == label:
-                self.from_line = lineno
-        if isinstance(self.to_line, str):
-            if self.to_line == label:
-                self.to_line = lineno
-
-    def has_labels(self):
-        return len(self.get_label_args()) > 0
-
-    def get_label_args(self):
-        return [label for label in (self.from_line, self.to_line)
-                      if isinstance(label, str)]
-
     def eval(self):
         raise NotImplementedError('DexLimitSteps commands cannot be evaled.')
 
diff --git a/dexter/feature_tests/subtools/test/err_bad_label_ref.cpp b/dexter/feature_tests/subtools/test/err_bad_label_ref.cpp
new file mode 100644
index 0000000..424edaa
--- /dev/null
+++ b/dexter/feature_tests/subtools/test/err_bad_label_ref.cpp
@@ -0,0 +1,14 @@
+// Purpose:
+//      Check that referencing an undefined label gives a useful error message.
+//
+// RUN: not %dexter_regression_test -v -- %s | FileCheck %s --match-full-lines
+//
+// CHECK: parser error:{{.*}}err_bad_label_ref.cpp(14): Unresolved label: 'label_does_not_exist'
+// CHECK-NEXT: {{Dex}}ExpectWatchValue('result', '0', on_line=ref('label_does_not_exist'))
+
+int main() {
+    int result = 0;
+    return result;
+}
+
+// DexExpectWatchValue('result', '0', on_line=ref('label_does_not_exist'))
diff --git a/dexter/feature_tests/subtools/test/err_duplicate_label.cpp b/dexter/feature_tests/subtools/test/err_duplicate_label.cpp
new file mode 100644
index 0000000..7da6920
--- /dev/null
+++ b/dexter/feature_tests/subtools/test/err_duplicate_label.cpp
@@ -0,0 +1,12 @@
+// Purpose:
+//      Check that defining duplicate labels gives a useful error message.
+//
+// RUN: not %dexter_regression_test -v -- %s | FileCheck %s --match-full-lines
+//
+// CHECK: parser error:{{.*}}err_duplicate_label.cpp(11): Found duplicate line label: 'oops'
+// CHECK-NEXT: {{Dex}}Label('oops')
+
+int main() {
+    int result = 0; // DexLabel('oops')
+    return result;  // DexLabel('oops')
+}
diff --git a/dexter/feature_tests/subtools/test/label_offset.cpp b/dexter/feature_tests/subtools/test/label_offset.cpp
new file mode 100644
index 0000000..81d4ca4
--- /dev/null
+++ b/dexter/feature_tests/subtools/test/label_offset.cpp
@@ -0,0 +1,24 @@
+// Purpose:
+//      Check that we can use label-relative line numbers.
+//
+// RUN: %dexter_regression_test -v -- %s | FileCheck %s
+//
+// CHECK: label_offset.cpp: (1.0000)
+
+int main() {  // DexLabel('main')
+    int var = 0;
+    var = var;
+    return 0;
+}
+
+/*
+DexExpectWatchValue('var', '0', from_line=ref('main')+2, to_line=ref('main')+3)
+DexExpectProgramState({
+    'frames': [
+        {
+            'location': { 'lineno': ref('main')+2 },
+            'watches': { 'var': '0' }
+        }
+    ]
+})
+*/