diff --git a/mypy/options.py b/mypy/options.py
index 38072b821d15..479979bdaa60 100644
--- a/mypy/options.py
+++ b/mypy/options.py
@@ -2,6 +2,7 @@
 import re
 import pprint
 import sys
+import platform
 
 from typing_extensions import Final
 from typing import Dict, List, Mapping, Optional, Pattern, Set, Tuple, Callable, Any
@@ -71,6 +72,7 @@ def __init__(self) -> None:
         # then mypy does not search for PEP 561 packages.
         self.python_executable = sys.executable  # type: Optional[str]
         self.platform = sys.platform
+        self.platform_system = platform.system()
         self.custom_typing_module = None  # type: Optional[str]
         self.custom_typeshed_dir = None  # type: Optional[str]
         self.mypy_path = []  # type: List[str]
diff --git a/mypy/reachability.py b/mypy/reachability.py
index 5ee813dc982c..52011c5be498 100644
--- a/mypy/reachability.py
+++ b/mypy/reachability.py
@@ -1,5 +1,4 @@
 """Utilities related to determining the reachability of code (in semantic analysis)."""
-
 from typing import Tuple, TypeVar, Union, Optional
 from typing_extensions import Final
 
@@ -92,7 +91,7 @@ def infer_condition_value(expr: Expression, options: Options) -> int:
     else:
         result = consider_sys_version_info(expr, pyversion)
         if result == TRUTH_VALUE_UNKNOWN:
-            result = consider_sys_platform(expr, options.platform)
+            result = consider_sys_platform(expr, options.platform,options.platform_system)
     if result == TRUTH_VALUE_UNKNOWN:
         if name == 'PY2':
             result = ALWAYS_TRUE if pyversion[0] == 2 else ALWAYS_FALSE
@@ -150,8 +149,8 @@ def consider_sys_version_info(expr: Expression, pyversion: Tuple[int, ...]) -> i
     return TRUTH_VALUE_UNKNOWN
 
 
-def consider_sys_platform(expr: Expression, platform: str) -> int:
-    """Consider whether expr is a comparison involving sys.platform.
+def consider_sys_platform(expr: Expression, platform: str, platform_system: str) -> int:
+    """Consider whether expr is a comparison involving sys.platform and platform.system()
 
     Return ALWAYS_TRUE, ALWAYS_FALSE, or TRUTH_VALUE_UNKNOWN.
     """
@@ -166,9 +165,14 @@ def consider_sys_platform(expr: Expression, platform: str) -> int:
         op = expr.operators[0]
         if op not in ('==', '!='):
             return TRUTH_VALUE_UNKNOWN
-        if not is_sys_attr(expr.operands[0], 'platform'):
-            return TRUTH_VALUE_UNKNOWN
-        right = expr.operands[1]
+        # check if either platform or platform_system is being used
+        if platform_system:
+            if not is_platform_attr(expr.operands[0], 'platform_system'):
+                return TRUTH_VALUE_UNKNOWN
+        elif platform:
+            if not is_sys_attr(expr.operands[0], 'platform'):
+                return TRUTH_VALUE_UNKNOWN
+            right = expr.operands[1]
         if not isinstance(right, (StrExpr, UnicodeExpr)):
             return TRUTH_VALUE_UNKNOWN
         return fixed_comparison(platform, op, right.value)
@@ -261,6 +265,16 @@ def is_sys_attr(expr: Expression, name: str) -> bool:
     return False
 
 
+def is_platform_attr(expr: Expression, name: str) -> bool:
+    # Platform lib calls methods, it differs from sys lib
+    # sys.platform is of str class and platform.system is of
+    # function class
+    if isinstance(expr, MemberExpr) and expr.name == name:
+        if isinstance(expr.expr, CallExpr) and expr.expr.name == 'platform':
+            return True
+    return False
+
+
 def mark_block_unreachable(block: Block) -> None:
     block.is_unreachable = True
     block.accept(MarkImportsUnreachableVisitor())
diff --git a/test-data/unit/check-unreachable-code.test b/test-data/unit/check-unreachable-code.test
index 262ac86e49ad..c18fb12527df 100644
--- a/test-data/unit/check-unreachable-code.test
+++ b/test-data/unit/check-unreachable-code.test
@@ -302,6 +302,8 @@ else:
 import sys
 if sys.platform == 'fictional':
     def foo() -> int: return 0
+if platform.system() == 'fake':
+    def foo() -> int: return 0
 else:
     def foo() -> str: return ''
 foo() + ''