diff --git a/src/builtin_math.cpp b/src/builtin_math.cpp
index 6ae67677b..e6142f703 100644
--- a/src/builtin_math.cpp
+++ b/src/builtin_math.cpp
@@ -134,8 +134,8 @@ static const wchar_t *math_describe_error(te_error_t &error) {
     switch (error.type) {
         case TE_ERROR_NONE:
             DIE("Error has no position");
-        case TE_ERROR_UNKNOWN_VARIABLE:
-            return _(L"Unknown variable");
+        case TE_ERROR_UNKNOWN_FUNCTION:
+            return _(L"Unknown function");
         case TE_ERROR_MISSING_CLOSING_PAREN:
             return _(L"Missing closing parenthesis");
         case TE_ERROR_MISSING_OPENING_PAREN:
diff --git a/src/tinyexpr.cpp b/src/tinyexpr.cpp
index 035ea15b9..e134b6cb7 100644
--- a/src/tinyexpr.cpp
+++ b/src/tinyexpr.cpp
@@ -91,7 +91,7 @@ typedef struct state {
     te_error_type_t error;
 } state;
 
-/* Parses the input expression and binds variables. */
+/* Parses the input expression. */
 /* Returns NULL on error. */
 te_expr *te_compile(const char *expression, te_error_t *error);
 
@@ -234,7 +234,7 @@ void next_token(state *s) {
             s->value = strtod(s->next, const_cast<char **>(&s->next));
             s->type = TOK_NUMBER;
         } else {
-            /* Look for a variable or builtin function call. */
+            /* Look for a function call. */
             // But not when it's an "x" followed by whitespace
             // - that's the alternative multiplication operator.
             if (s->next[0] >= 'a' && s->next[0] <= 'z' &&
@@ -260,7 +260,7 @@ void next_token(state *s) {
                 } else if (s->type != TOK_ERROR || s->error == TE_ERROR_UNKNOWN) {
                     // Our error is more specific, so it takes precedence.
                     s->type = TOK_ERROR;
-                    s->error = TE_ERROR_UNKNOWN_VARIABLE;
+                    s->error = TE_ERROR_UNKNOWN_FUNCTION;
                 }
             } else {
                 /* Look for an operator or special character. */
@@ -329,7 +329,7 @@ static te_expr *expr(state *s);
 static te_expr *power(state *s);
 
 static te_expr *base(state *s) {
-    /* <base>      =    <constant> | <variable> | <function-0> {"(" ")"} | <function-1> <power> |
+    /* <base>      =    <constant> | <function-0> {"(" ")"} | <function-1> <power> |
      * <function-X> "(" <expr> {"," <expr>} ")" | "(" <list> ")" */
     te_expr *ret;
     int arity;
diff --git a/src/tinyexpr.h b/src/tinyexpr.h
index bd6e93409..fec012fd4 100644
--- a/src/tinyexpr.h
+++ b/src/tinyexpr.h
@@ -29,7 +29,7 @@
 
 typedef enum {
     TE_ERROR_NONE = 0,
-    TE_ERROR_UNKNOWN_VARIABLE = 1,
+    TE_ERROR_UNKNOWN_FUNCTION = 1,
     TE_ERROR_MISSING_CLOSING_PAREN = 2,
     TE_ERROR_MISSING_OPENING_PAREN = 3,
     TE_ERROR_TOO_FEW_ARGS = 4,
diff --git a/tests/checks/math.fish b/tests/checks/math.fish
index 381a26bed..b3cab0c4a 100644
--- a/tests/checks/math.fish
+++ b/tests/checks/math.fish
@@ -127,7 +127,7 @@ math 0x2 # Hex
 math 5 x 4
 math 2x 4
 math 2 x4 # ERROR
-# CHECKERR: math: Error: Unknown variable
+# CHECKERR: math: Error: Unknown function
 # CHECKERR: '2 x4'
 # CHECKERR:     ^
 math 0x 3