diff --git a/moorpy/helpers.py b/moorpy/helpers.py
index 05b4aa9..76cf6bd 100644
--- a/moorpy/helpers.py
+++ b/moorpy/helpers.py
@@ -671,14 +671,16 @@ def getLineProps(dnommm, material, lineProps=None, source=None, name="", rho=102
     # Shorthand for the sub-dictionary of properties for the material in question  
     mat = lineProps[material]       
     
+    # convert nominal diameter from mm to m (needed for the range checks below)
+    d = dnommm*0.001
+
     # Check valid diameter ranges
     if mat['d_max'] >= 0 and d > mat['d_max']: # if a max value is given and the diameter is greater than the max
         raise Exception(f"Input diameter {d} m is greater than the max valid value of {mat['d_max']} m for {material}.")
     if mat['d_min'] >= 0 and d < mat['d_min']: # if a min value is given and the diameter is less than the min
         raise Exception(f"Input diameter {d} m is less than the min valid value of {mat['d_min']} m for {material}.")
-        
+
     # calculate the relevant properties for this specific line type
-    d = dnommm*0.001                # convert nominal diameter from mm to m      
     mass = mat['mass_d2']*d**2
        
     MBL  = mat[ 'MBL_0'] + mat[ 'MBL_d']*d + mat[ 'MBL_d2']*d**2 + mat[ 'MBL_d3']*d**3 
@@ -841,7 +843,7 @@ def loadLineProps(source):
         output[mat]['cost_EA'  ] = getFromDict(props, 'cost_EA'  , default=0.0)
         output[mat]['cost_MBL' ] = getFromDict(props, 'cost_MBL' , default=0.0)
         output[mat]['d_min'    ] = getFromDict(props, 'd_min'    , default=-1.0) # -1 to disable checking
-        output[mat]['d_max'    ] = getFromDict(props, 'd_dmax'   , default=-1.0) # -1 to disable checking
+        output[mat]['d_max'    ] = getFromDict(props, 'd_max'    , default=-1.0) # -1 to disable checking
 
     return output
 
diff --git a/tests/test_line.py b/tests/test_line.py
index c9b0ea6..00678c5 100644
--- a/tests/test_line.py
+++ b/tests/test_line.py
@@ -18,9 +18,37 @@
 
 def test_line_stiffness():
     '''Checks stiffness of mooring lines.'''
-       
-       
-       
+
+
+def test_getLineProps_diameter_limits():
+    '''getLineProps must apply the d_min / d_max range checks correctly.
+
+    Regression test for two bugs in the diameter validation:
+      1. ``d`` (the diameter in metres) was referenced in the range checks
+         before it was assigned, so any material with ``d_min >= 0`` or
+         ``d_max >= 0`` raised ``UnboundLocalError`` instead of the intended
+         range Exception.
+      2. ``loadLineProps`` read ``d_max`` from the key ``'d_dmax'`` (a typo),
+         so a user-specified ``d_max`` was silently dropped to the -1
+         "disabled" default and the upper-bound check never fired.
+    '''
+    base = {'mass_d2': 100.0, 'MBL_0': 0.0, 'MBL_d': 1e6}
+
+    # within the valid range -> succeeds and returns a line type dict
+    src = {'lineProps': {'rope': {**base, 'd_min': 0.01, 'd_max': 0.20}}}
+    lt = getLineProps(50.0, 'rope', source=src)  # 50 mm = 0.05 m, in range
+    assert isinstance(lt, dict) and lt['material'] == 'rope'
+
+    # below d_min -> the intended Exception (not UnboundLocalError)
+    with pytest.raises(Exception, match='less than the min'):
+        getLineProps(5.0, 'rope', source=src)    # 5 mm = 0.005 m < 0.01
+
+    # above d_max -> the intended Exception; this only works if the d_max
+    # typo is fixed (otherwise d_max stays -1 and the check is disabled)
+    with pytest.raises(Exception, match='greater than the max'):
+        getLineProps(300.0, 'rope', source=src)  # 300 mm = 0.3 m > 0.20
+
+
 if __name__ == '__main__':
     
     import moorpy as mp