diff --git a/php_decimal.c b/php_decimal.c
index 4871780..cbcb9c3 100644
--- a/php_decimal.c
+++ b/php_decimal.c
@@ -2373,7 +2373,10 @@ PHP_DECIMAL_ARGINFO_END()
 PHP_DECIMAL_METHOD(isPositive)
 {
     PHP_DECIMAL_PARAMS_PARSE_NONE();
-    RETURN_BOOL(mpd_ispositive(THIS_MPD()));
+
+    mpd_t *mpd = THIS_MPD();
+
+    RETURN_BOOL(!mpd_isnan(mpd) && mpd_ispositive(mpd));
 }
 
 /**
@@ -2384,7 +2387,10 @@ PHP_DECIMAL_ARGINFO_END()
 PHP_DECIMAL_METHOD(isNegative)
 {
     PHP_DECIMAL_PARAMS_PARSE_NONE();
-    RETURN_BOOL(mpd_isnegative(THIS_MPD()));
+
+    mpd_t *mpd = THIS_MPD();
+
+    RETURN_BOOL(!mpd_isnan(mpd) && mpd_isnegative(mpd));
 }
 
 /**
diff --git a/tests/php7/methods/isNegative.phpt b/tests/php7/methods/isNegative.phpt
new file mode 100644
index 0000000..b181342
--- /dev/null
+++ b/tests/php7/methods/isNegative.phpt
@@ -0,0 +1,55 @@
+--TEST--
+Decimal::isNegative
+--SKIPIF--
+<?php
+if (!extension_loaded("decimal")) echo "skip";
+?>
+--FILE--
+<?php
+use Decimal\Decimal;
+
+/**
+ * Shortcut to construct a new decimal.
+ */
+function decimal(...$args) { return new Decimal(...$args); }
+
+$tests = [
+    /* Number, expected */
+
+    [ "1E-50",  false],
+    ["-1E-50",  true],
+
+    ["0",       false],
+    ["-0",      true],
+    [1,         false],
+    [2,         false],
+    [3,         false],
+
+    [-1,        true],
+    [-2,        true],
+    [-3,        true],
+
+    ["1.5",     false],
+    ["2.5",     false],
+    ["3.5",     false],
+
+    ["-1.5",    true],
+    ["-2.5",    true],
+    ["-3.5",    true],
+
+    [ "NAN",    false],
+    [ "INF",    false],
+    ["-INF",    true],
+];
+
+foreach ($tests as $pair) {
+    $number = $pair[0];
+    $expect = $pair[1];
+    $result = decimal($number)->isNegative();
+
+    if ((string) $result !== (string) $expect) {
+        print_r(compact("number", "result", "expect"));
+    }
+}
+?>
+--EXPECT--
diff --git a/tests/php7/methods/isPositive.phpt b/tests/php7/methods/isPositive.phpt
new file mode 100644
index 0000000..96e0fc2
--- /dev/null
+++ b/tests/php7/methods/isPositive.phpt
@@ -0,0 +1,55 @@
+--TEST--
+Decimal::isPositive
+--SKIPIF--
+<?php
+if (!extension_loaded("decimal")) echo "skip";
+?>
+--FILE--
+<?php
+use Decimal\Decimal;
+
+/**
+ * Shortcut to construct a new decimal.
+ */
+function decimal(...$args) { return new Decimal(...$args); }
+
+$tests = [
+    /* Number, expected */
+
+    [ "1E-50",  true],
+    ["-1E-50",  false],
+
+    ["0",       true],
+    ["-0",      false],
+    [1,         true],
+    [2,         true],
+    [3,         true],
+
+    [-1,        false],
+    [-2,        false],
+    [-3,        false],
+
+    ["1.5",     true],
+    ["2.5",     true],
+    ["3.5",     true],
+
+    ["-1.5",    false],
+    ["-2.5",    false],
+    ["-3.5",    false],
+
+    [ "NAN",    false],
+    [ "INF",    true],
+    ["-INF",    false],
+];
+
+foreach ($tests as $pair) {
+    $number = $pair[0];
+    $expect = $pair[1];
+    $result = decimal($number)->isPositive();
+
+    if ((string) $result !== (string) $expect) {
+        print_r(compact("number", "result", "expect"));
+    }
+}
+?>
+--EXPECT--