diff --git a/src/parse/control_flow.rs b/src/parse/control_flow.rs
index 227ef72..77477eb 100644
--- a/src/parse/control_flow.rs
+++ b/src/parse/control_flow.rs
@@ -156,7 +156,6 @@ impl<'a> Parser<'a> {
 
     pub(super) fn parse_for(&mut self) -> SassResult<Vec<Stmt>> {
         self.whitespace_or_comment();
-        // todo: test for error here
         self.expect_char('$')?;
 
         let var = self
@@ -236,14 +235,16 @@ impl<'a> Parser<'a> {
         self.whitespace_or_comment();
         let from_val = self.parse_value_from_vec(from_toks, true)?;
         let from = match from_val.node {
-            Value::Dimension(Some(n), ..) => match n.to_integer().to_isize() {
+            Value::Dimension(Some(n), ..) => match n.to_i32() {
+                Some(std::i32::MAX) | None => {
+                    return Err((format!("{} is not an int.", n), from_val.span).into())
+                }
                 Some(v) => v,
-                None => return Err((format!("{} is not a int.", n), from_val.span).into()),
             },
-            Value::Dimension(None, ..) => todo!(),
+            Value::Dimension(None, ..) => return Err(("NaN is not an int.", from_val.span).into()),
             v => {
                 return Err((
-                    format!("{} is not an integer.", v.inspect(from_val.span)?),
+                    format!("{} is not a number.", v.inspect(from_val.span)?),
                     from_val.span,
                 )
                     .into())
@@ -252,14 +253,16 @@ impl<'a> Parser<'a> {
 
         let to_val = self.parse_value(true, &|_| false)?;
         let to = match to_val.node {
-            Value::Dimension(Some(n), ..) => match n.to_integer().to_isize() {
+            Value::Dimension(Some(n), ..) => match n.to_i32() {
+                Some(std::i32::MAX) | None => {
+                    return Err((format!("{} is not an int.", n), to_val.span).into())
+                }
                 Some(v) => v,
-                None => return Err((format!("{} is not a int.", n), to_val.span).into()),
             },
-            Value::Dimension(None, ..) => todo!(),
+            Value::Dimension(None, ..) => return Err(("NaN is not an int.", from_val.span).into()),
             v => {
                 return Err((
-                    format!("{} is not an integer.", v.to_css_string(to_val.span)?),
+                    format!("{} is not a number.", v.to_css_string(to_val.span)?),
                     to_val.span,
                 )
                     .into())
@@ -269,12 +272,13 @@ impl<'a> Parser<'a> {
         self.expect_char('{')?;
 
         let body = read_until_closing_curly_brace(self.toks)?;
-        self.toks.next();
+
+        self.expect_char('}')?;
 
         let (mut x, mut y);
         // we can't use an inclusive range here
         #[allow(clippy::range_plus_one)]
-        let iter: &mut dyn Iterator<Item = isize> = if from < to {
+        let iter: &mut dyn Iterator<Item = i32> = if from < to {
             x = from..(to + through);
             &mut x
         } else {
diff --git a/src/value/number/mod.rs b/src/value/number/mod.rs
index 522f915..f65952b 100644
--- a/src/value/number/mod.rs
+++ b/src/value/number/mod.rs
@@ -318,6 +318,42 @@ impl fmt::Debug for Number {
     }
 }
 
+impl ToPrimitive for Number {
+    fn to_u64(&self) -> Option<u64> {
+        match self {
+            Self::Small(n) => {
+                if !n.denom().is_one() {
+                    return None;
+                }
+                n.to_u64()
+            }
+            Self::Big(n) => {
+                if !n.denom().is_one() {
+                    return None;
+                }
+                n.to_u64()
+            }
+        }
+    }
+
+    fn to_i64(&self) -> Option<i64> {
+        match self {
+            Self::Small(n) => {
+                if !n.denom().is_one() {
+                    return None;
+                }
+                n.to_i64()
+            }
+            Self::Big(n) => {
+                if !n.denom().is_one() {
+                    return None;
+                }
+                n.to_i64()
+            }
+        }
+    }
+}
+
 impl Display for Number {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let mut whole = self.to_integer().abs();
diff --git a/tests/for.rs b/tests/for.rs
index 820591a..8e5d069 100644
--- a/tests/for.rs
+++ b/tests/for.rs
@@ -118,3 +118,51 @@ test!(
     "  /**/  @for  /**/  $i  /**/  from  /**/  0  /**/  to  /**/  2  /**/  {}  /**/  ",
     "/**/\n/**/\n"
 );
+test!(
+    uppercase_keywords,
+    "@for $i FROM 0 TO 2 {
+        @foo;
+    }",
+    "@foo;\n@foo;\n"
+);
+error!(
+    missing_keyword_from,
+    "@for $i fro", "Error: Expected \"from\"."
+);
+error!(missing_dollar_sign, "@for", "Error: expected \"$\".");
+error!(
+    variable_missing_identifier,
+    "@for $", "Error: Expected identifier."
+);
+error!(
+    from_value_is_decimal,
+    "@for $i from 0.5 to 2 {}", "Error: 0.5 is not an int."
+);
+error!(
+    to_value_is_decimal,
+    "@for $i from 0 to 1.5 {}", "Error: 1.5 is not an int."
+);
+error!(
+    from_value_is_non_numeric,
+    "@for $i from red to 2 {}", "Error: red is not a number."
+);
+error!(
+    to_value_is_non_numeric,
+    "@for $i from 0 to red {}", "Error: red is not a number."
+);
+error!(
+    through_i32_max,
+    "@for $i from 0 through 2147483647 {}", "Error: 2147483647 is not an int."
+);
+error!(
+    from_i32_max,
+    "@for $i from 2147483647 through 0 {}", "Error: 2147483647 is not an int."
+);
+error!(
+    from_nan,
+    "@for $i from (0/0) through 0 {}", "Error: NaN is not an int."
+);
+error!(
+    to_nan,
+    "@for $i from 0 through (0/0) {}", "Error: NaN is not an int."
+);