diff --git a/README.md b/README.md
index 808f4ae..fd381ef 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,10 @@ Rhapsody is published on [PyPI](https://pypi.org/). To install Rhapsody, please
 ```console
 $ pip install -U prody-rhapsody
 ```
+It might be necessary to manually install the DSSP program, by giving for instance on Linux:
+```console
+$ sudo apt get dssp
+```
 
 ## Install from source
 Rhapsody is written in pure Python so no local compilation is needed.
diff --git a/rhapsody/PDB.py b/rhapsody/PDB.py
index 3008b26..ebe494a 100644
--- a/rhapsody/PDB.py
+++ b/rhapsody/PDB.py
@@ -348,15 +348,15 @@ def calcANMfeatures(self, chain='all', env='chain',
     def _launchDSSP(self, ag):
         LOGGER.info('Running DSSP...')
         LOGGER.timeit('_DSSP')
+        pdb_file = writePDB('_temp.pdb', ag, secondary=False)
         try:
-            pdb_file  = writePDB('_temp.pdb', ag, secondary=False)
             dssp_file = execDSSP(pdb_file, outputname='_temp')
-            ag = parseDSSP(dssp_file, ag)
-        except:
-            raise
-        finally:
-            os.remove('_temp.pdb')
-            os.remove('_temp.dssp')
+        except EnvironmentError:
+            raise EnvironmentError("dssp executable not found: please install "
+                                   "with 'sudo apt install dssp'")
+        ag = parseDSSP(dssp_file, ag)
+        os.remove('_temp.pdb')
+        os.remove('_temp.dssp')
         LOGGER.report('DSSP finished in %.1fs.', '_DSSP')
         return ag
 
diff --git a/setup.py b/setup.py
index d246243..0269ecd 100644
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,7 @@
     version=version,
     packages=find_packages(exclude=['contrib', 'docs', 'tests']),
     python_requires='>=3.5, <4',
-    install_requires=['requests', 'numpy', 'scikit-learn',
+    install_requires=['requests', 'numpy', 'scikit-learn', 'matplotlib',
                       'biopython', 'pyparsing', 'prody'],
     description="""Python program, based on ProDy, for pathogenicity prediction
     of human missense variants.""",