diff --git a/nmapui/validation.py b/nmapui/validation.py
index 199ecf0f..db9aae70 100644
--- a/nmapui/validation.py
+++ b/nmapui/validation.py
@@ -7,6 +7,26 @@
     r"^[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?"
     r"(\.[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)*$"
 )
+_IPV4_LIKE_RE = re.compile(r"^[0-9./-]+$")
+
+
+def _is_valid_ipv4_range(item: str) -> bool:
+    """Return whether an item is an Nmap-style IPv4 octet range."""
+    octets = item.split(".")
+    if len(octets) != 4 or not any("-" in octet for octet in octets):
+        return False
+
+    for octet in octets:
+        bounds = octet.split("-")
+        if len(bounds) > 2 or any(not bound.isdigit() for bound in bounds):
+            return False
+        values = [int(bound) for bound in bounds]
+        if any(value > 255 for value in values):
+            return False
+        if len(values) == 2 and values[0] > values[1]:
+            return False
+
+    return True
 
 
 def _is_valid_item(item: str) -> tuple[bool, str | None]:
@@ -27,6 +47,14 @@ def _is_valid_item(item: str) -> tuple[bool, str | None]:
     except ValueError:
         pass
 
+    # Nmap supports ranges within IPv4 octets, such as 192.168.1.1-254.
+    if _is_valid_ipv4_range(item):
+        return True, None
+
+    # Do not let malformed dotted IPs fall through and pass as hostnames.
+    if _IPV4_LIKE_RE.fullmatch(item):
+        return False, f"Invalid target: {item}"
+
     # Hostname / FQDN (nmap accepts these natively)
     if _HOSTNAME_RE.match(item):
         return True, None
diff --git a/tests/test_validation.py b/tests/test_validation.py
new file mode 100644
index 00000000..e1dd0138
--- /dev/null
+++ b/tests/test_validation.py
@@ -0,0 +1,35 @@
+import pytest
+
+from nmapui.validation import validate_target
+
+
+@pytest.mark.parametrize(
+    "target",
+    [
+        "192.168.1.1",
+        "192.168.1.0/24",
+        "192.168.1.1-254",
+        "10-12.0.0.1-20",
+        "scanme.nmap.org",
+        "192.168.1.1, 10.0.0.0/8",
+    ],
+)
+def test_validate_target_accepts_supported_target_formats(target):
+    assert validate_target(target) == (True, None)
+
+
+@pytest.mark.parametrize(
+    "target",
+    [
+        "192.168.1.999",
+        "192.168.1",
+        "192.168.1.1/33",
+        "192.168.1.254-1",
+        "192.168.1.1-999",
+    ],
+)
+def test_validate_target_rejects_malformed_ip_like_targets(target):
+    valid, error = validate_target(target)
+
+    assert valid is False
+    assert error == f"Invalid target: {target}"