diff --git a/lib/std/math/isnormal.zig b/lib/std/math/isnormal.zig
index 0430e1367a..88e186a3c9 100644
--- a/lib/std/math/isnormal.zig
+++ b/lib/std/math/isnormal.zig
@@ -9,19 +9,19 @@ pub fn isNormal(x: anytype) bool {
     switch (T) {
         f16 => {
             const bits = @bitCast(u16, x);
-            return (bits + (1 << 10)) & (maxInt(u16) >> 1) >= (1 << 11);
+            return (bits +% (1 << 10)) & (maxInt(u16) >> 1) >= (1 << 11);
         },
         f32 => {
             const bits = @bitCast(u32, x);
-            return (bits + (1 << 23)) & (maxInt(u32) >> 1) >= (1 << 24);
+            return (bits +% (1 << 23)) & (maxInt(u32) >> 1) >= (1 << 24);
         },
         f64 => {
             const bits = @bitCast(u64, x);
-            return (bits + (1 << 52)) & (maxInt(u64) >> 1) >= (1 << 53);
+            return (bits +% (1 << 52)) & (maxInt(u64) >> 1) >= (1 << 53);
         },
         f128 => {
             const bits = @bitCast(u128, x);
-            return (bits + (1 << 112)) & (maxInt(u128) >> 1) >= (1 << 113);
+            return (bits +% (1 << 112)) & (maxInt(u128) >> 1) >= (1 << 113);
         },
         else => {
             @compileError("isNormal not implemented for " ++ @typeName(T));
@@ -34,6 +34,18 @@ test "math.isNormal" {
     try expect(!isNormal(math.nan(f32)));
     try expect(!isNormal(math.nan(f64)));
     try expect(!isNormal(math.nan(f128)));
+    try expect(!isNormal(-math.nan(f16)));
+    try expect(!isNormal(-math.nan(f32)));
+    try expect(!isNormal(-math.nan(f64)));
+    try expect(!isNormal(-math.nan(f128)));
+    try expect(!isNormal(math.inf(f16)));
+    try expect(!isNormal(math.inf(f32)));
+    try expect(!isNormal(math.inf(f64)));
+    try expect(!isNormal(math.inf(f128)));
+    try expect(!isNormal(-math.inf(f16)));
+    try expect(!isNormal(-math.inf(f32)));
+    try expect(!isNormal(-math.inf(f64)));
+    try expect(!isNormal(-math.inf(f128)));
     try expect(!isNormal(@as(f16, 0)));
     try expect(!isNormal(@as(f32, 0)));
     try expect(!isNormal(@as(f64, 0)));