diff --git a/MANUAL.md b/MANUAL.md
index 906433f..d7fa290 100644
--- a/MANUAL.md
+++ b/MANUAL.md
@@ -102,7 +102,7 @@ rpn>
 |hex|	hexadecimal representation
 |prec|	get float precision in bits when first stack is not a number, set float precision in bits when first stack entry is a number. ex: ```256 prec```
 |round|	set float rounding mode. Authoerized values are: ```["nearest", "toward zero", "toward +inf", "toward -inf", "away from zero"] round```. ex: ```"nearest" round```
-|sign|	1 if number at stack level 1 is > 0, 0 if == 0, -1 if <= 0
+|sign|	sign of a real, unary vector in the same direction for a complex
 
 ### real
 
diff --git a/src/rpn-real.hpp b/src/rpn-real.hpp
index eecd3be..f85e5b1 100644
--- a/src/rpn-real.hpp
+++ b/src/rpn-real.hpp
@@ -410,12 +410,23 @@ void fact()
 void sign()
 {
     MIN_ARGUMENTS(1);
-    ARG_MUST_BE_OF_TYPE(0, cmd_number);
 
-    // fact(n) = gamma(n+1)
-    number* left = (number*)_stack->back();
-    int result = mpfr_sgn(left->_value.mpfr);
-    left->_value = (long)result;
+    if (_stack->get_type(0) == cmd_number)
+    {        
+        // fact(n) = gamma(n+1)
+        number* left = (number*)_stack->back();
+        int result = mpfr_sgn(left->_value.mpfr);
+        left->_value = (long)result;
+    }
+    else if (_stack->get_type(0) == cmd_complex)
+    {
+        // calc x/sqrt(x*x+y*y) +iy/sqrt(x*x+y*y)
+        dup();
+        rpn_abs();
+        div();
+    }
+    else
+        ERR_CONTEXT(ret_bad_operand_type);
 }
 
 void mant()
diff --git a/test/10-complex.txt b/test/10-complex.txt
index 75deefe..a8a2d53 100644
--- a/test/10-complex.txt
+++ b/test/10-complex.txt
@@ -146,3 +146,18 @@ drop
 (3,4) abs
 -> stack should be 5
 drop
+
+# sign (1)
+(1,0) sign
+-> stack should be (1,0)
+drop
+
+# sign (2)
+(0,1) sign
+-> stack should be (0,1)
+drop
+
+# sign (3)
+(3,-4) sign
+-> stack should be (0.6,-0.8)
+drop