diff --git a/packages/pride-ppp/src/pride_ppp/factories/output.py b/packages/pride-ppp/src/pride_ppp/factories/output.py
index 04aaddf..bf66995 100644
--- a/packages/pride-ppp/src/pride_ppp/factories/output.py
+++ b/packages/pride-ppp/src/pride_ppp/factories/output.py
@@ -80,15 +80,27 @@ def get_wrms_from_res(res_path):
                 line = res_file.readline()
                 line_data = line.split()
                 while not line.startswith("TIM"):
-                    phase_residual = float(line_data[1])
-                    phase_weight = float(line_data[3].replace("D", "E"))
-                    sumOfSquares += phase_residual**2 * phase_weight
-                    sumOfWeights += phase_weight
+                    try:
+                        phase_residual = float(line_data[1])
+                        phase_weight = float(line_data[3].replace("D", "E"))
+                    except (ValueError, IndexError):
+                        # PRIDE-PPPAR writes residuals in fixed-width columns; an
+                        # unusually large value (e.g. an unresolved ambiguity) can
+                        # overflow its column and run into the neighbouring field
+                        # with no separating space (e.g. "0.0000-1641.5825"),
+                        # which breaks whitespace-based splitting. Skip just this
+                        # satellite's contribution rather than failing the epoch.
+                        logger.warning(
+                            f"Skipping unparsable residual line in {res_path}: {line.strip()!r}"
+                        )
+                    else:
+                        sumOfSquares += phase_residual**2 * phase_weight
+                        sumOfWeights += phase_weight
                     line = res_file.readline()
                     if line == "":
                         break
                     line_data = line.split()
-                wrms = (sumOfSquares / sumOfWeights) ** 0.5 * 1000  # in mm
+                wrms = (sumOfSquares / sumOfWeights) ** 0.5 * 1000 if sumOfWeights else float("nan")  # in mm
                 data.append(wrms)
             else:
                 line = res_file.readline()